Is your PC connected to the router by a cable or wifi?
Is your router plugged into the main (master) socket where the BT line first enters your house, or an extension lead/socket?
Try plugging the router into the master socket and connecting your PC/laptop to it with an ethernet cable and then run the TT speed test here
http://myaccount.talktalk.co.uk/speed-checker/
This will tell you if you have a decent connection or not.
If you still have problems, Try a different laptop - does that work OK?
You need to be careful to eliminate problems within your own control before reporting a fault to TT - they can (and will) charge for putting right stuff that is due to your equipment.