My Internet just stopped working
1) Unless you are on fibre, you are at the mercy of the BT wires. Some of these go back 100 years. So if the BT guy is in your street - and ESPECIALLY if he has a ladder - start to panic now.
You need to speak to the guy now - because once he gets back to the office, any fault you report will be added to the end of the queue. See below for more on this subject
2) Reboot your PC. If that fails to fix it, reboot your Router.
If your Router can't connect to the internet, your ISP may be 'down' - in which case chances are your phone 'land-line' is also dead. Most manage to sort themselves out within an hour or two, so wait a bit before ringing them on your mobile. NB. If you do ring your ISP and get told 'Your position in the queue is 99' just hang up. Let one of the other 98 callers tell them that their system is 'down'
Why is my Internet so slow ?
Internet speed problems are caused by almost anything. So before ringing your ISP (or BT) try to narrow down the problem yourself. Chances are you can fix it this week, whilst your ISP / BT will not fix it this year
WiFi problem ?
Start by connecting your PC direct to your Router using an Ethernet cable. If your Internet gets faster, then the problem is your WiFi, not your Router, BT wires or anything else
Interference
If your neighbours just installed WiFi, and yours got slower, then it's likely you have an interference problem
Many modern Routers will have a 'diagnostics' menu - or 'Station Search' menu - from which you can discover what frequency 'bands' are being used by your neighbours. Most Routers default to band '1'. So if your neighbours are using '1', switch to '6' - if '6' is used, switch to '12'. If all are used, work out which of your neighbours WiFi's are the 'weakest' (fewest 'bars') and select that one.
In the 'old days' things like your Microwave oven could effect your WiFi. Today kitchen equipment is much better shielded. However if you loose WiFi every time some-one uses your Microwave oven, that shielding isn't working and you should replace it (before it fries your eyeballs)
Software problems
Every time Microsoft or some other application performs an 'update' it can effect how your PC uses the internet. Commercial applications (Adobe in particular) have a habit of 'phoning home' at every opportunity and can get upset when your Firewall denies them access to the internet
A1. Identify the Ethernet chip-set built into your motherboard - and then go and get the latest drivers direct from the chip manufacturer (most likely Intel). Most system manufacturers (eg Dell) ship products with drivers that are already out-of-date .. others ship with 'OEM' versions of the driver that do not offer many of the vital options (such as setting 'buffer' sizes)
Dell has little interest in 'updating' drivers for 10 year old hardware - however Intel's 10 year old Ethernet chip-set may well be used in today's most modern motherboard (designers choose 'know working' parts, the older (and most bug free) the better). So Intel will continue to provide up-to-date drivers decades after Dell has lost interest. Once you have the latest drivers, go into the Hardware settings and increase all the buffer sizes etc. to the max.
A2. Windows XP automatically "assesses" the speed of your network card(s) and sets them accordingly. This 'auto-assessment' is performed again at regular intervals, so, no doubt, just like the 'Indexing Service', it will kick in unexpectedly and cause your system to slow to a crawl for no apparent reason. To prevent this, you should change all the 'automatic' settings (especially speed) of your network interfaces to some specific value.
Right click on 'My computer', select 'Manage', expand 'Device Manager' and 'Network adapters'. Right click the adapter and select 'Properties'. In the Advanced tab, check the various Properties. Any found set to 'auto' should be changed to something explicit (generally, the higher the value for 'Buffers' etc the better). For your Ethernet card, the most vital setting is 'Link Speed & Duplex' (this should be set to the maximum supported, typically '100Mbps/Full Duplex')
A3. Many Routers 'default' to 'standard' ADSL speeds (this may be shown as 'G.DMT'). Log-in to your Router as Admin and check yours and look for the 'ADSL2', or, better, 'ADSL2+' setting. If you can't find it, your Router may just be too old (although MOST will support ADSL2+ with a 'firmware' update)
Most Router manufacturers release new firmware (aka 'micro-code') at regular intervals. Note, however, that updating your Routers firmware could leave you with a 'bricked' unit .. so ONLY update the firmware if you have a problem - and be EXTREMELY sure you are getting the 'right' firmware version for your Router (check it's EXACT model name). Also make sure to get the "UK" firmware, NOT the "EU" (or "US" :-) ) version = the UK ADSL system uses different frequencies to most of Europe / USA !
A4. Finally, remember that WiFi will always be slower than a wired Ethernet cable = all PC's on WiFi have to 'share' the WiFi bandwidth (typically 56mbs), whilst each PC wired direct to the router gets it's own dedicated full bandwidth connection (typically 100mbs). So, for maximum speed (and minimum 'ping' latency) run a cable direct from the Router to your computer (& not via a Hub or Switch)
I've checked my NIC driver & Router etc. what else could it be ?
If you have checked your Router & updated all your drivers etc., the MOST likely problem is your actual phone wires. These can be so 'noisy' that your connection is very slow with a very low SNR (Signal to Noise Ratio), very high 'corrected blocks' (and even high 'uncorrected blocks') and your ISP might even be dropping your connection every few minutes - so check what your Router 'log' is telling you !
A1. Assuming your house is 'connected' using BT's ancient 'telephone wires', check on the BT site the 'expected' speed for your Post-Code.
If what you are getting is significantly lower than 'average', then the MOST LIKELY problem is your physical phone wires and how your actual phones are 'wired' (specifically, how extension phones are wired and/or your ADSL/Phone 'splitter' / 'Micro-filter')
Ideally you should have a BT style NTE5 'master' phone socket (the one connected to the outside wires) with the latest 'removable' split face-plate. If you have the older type without the 'split' plate, complain to BT - even if you have signed up to some other ISP, the 'master' socket is still BT's 'property' so you may be able to persuade them to replace it for free (especially if you hint you might switch back to using them :-) ).
A2. Each phone needs it's own separate 'micro-filter'. Any that are more than a few years old are likely to need replacing. Technology has moved on since the early days of broadband and current 'micro-filter' designs are a LOT more effective than those shipped even 3 years ago
Don't assume that yours are OK just because you have an ADSL-2 Router .. some of the early "ADSL-2" Routers were shipped with older style 'micro-filters' that limited your phone wires to less than 1 mbs !
A3. If you have wired 'extension' phones, the ancient 'bell' or 'ring' wire may be causing interference - look here for how to address this
Note that your house phone extension wiring may contain 4 twisted pairs, however only one pair is actually needed for the phone (and one more was used for the extension 'bell') - the other 5 wires are just 'smoke & mirrors' by the 'Post Office' to discourage customers from installing their own kit. See here for some guidance
A4. If you have done everything possible INSIDE your house, the chances are the problem is outside. To 'fix' this, a BT Engineer will have to be called out. If they decide that the problem is caused by you = inside your house, they will hit you with a fee (typically £120), so don't 'complain' to your ISP (& demand they call out BT) before exhausting all other possibilities !
Whist the 'street cabinet' likely uses proper IDC's (Insulation Displacement Connectors) to connect your line to the exchange, chances are the wires at the top of the pole across the street (and at the terminal block under your roof) don't.
Instead they likely go through some ancient 'screw terminal' blocks using brass washers and screws to 'clamp' the wires. The copper wires and brass washers can corrode together making a poor connection and the brass <%gt; copper 'join' can create a 'diode' effect. All this is bad news for ADSL (and for the BT guy who has to climb up the ladder to your roof, or the pole in the street, and replace them all with IDC's :-) )
NB. If you happen to see a BT Engineer 'up the pole' or fiddling around inside your local street cabinet, rush inside and check your Internet (especially the speed) !! Any time ANYTHING is 'disturbed' in the 'local loop', some fragile 50 year old copper wire connection could 'give up the ghost' - and it's far better to 'discuss' any problem with the BT Engineer now (when he can fix whatever he just broke) rather than spend the next 6 months watching your ISP and BT kick the problem back and forth as they argue about who's 'issue' it is