The fault is with your PC (or, more specifically, with its browser) and not with your internet connection, so BT won't be able to help.
If you're using Internet Explorer, you might need to re-install it. (Download the latest version from the Microsoft website or look for it on the 'free' coverdisks which come with some magazines). However, you could also try using System Restore, to take your PC's configuration back to a date before the problem first occurred.
Alternatively, just switch to using a different (and much better) browser, i.e. Firefox:
http://www.mozilla.com/en-US/
Chris