This question is being asked for my brother in law as he has the following problem. "I use IE7 & have just installed a new BT Router. All OK originally then I suddenly could not open either browser to get emails or get on the internet. My b'band connection is still working as I can use BT Talk. Have run AdAware & AVG antivirus with no harmful results showing & have Zonealarm as a firewall -all up to date. Since I can't get on internet, I can't reinstall IE7 or basically do anything. I'm beginning to think that a complete reinstall of XP with the resulting hassle of d'loading SP1 & SP2 & everything else may be the only way forward. As a side issue I also can't for some reason use System Restore. Any suggestions please."
As you state, it might eventually be necessary to re-install XP. However, before doing that, it might be worth while investing a few pounds, at your local newsagent's shop, purchasing one of the many PC magazines available. Just look through the list of contents of the cover disks and you're almost certain to find one which includes IE7 or, better, Firefox.
Once you've installed a browser, from the disk, you'll be able to get back online and attempt to sort out any remaining problems.