IE stopped working

My copy of IE 7 just stopped working. Just like that. This precipitated a general reinstall which was a bit overdue anyway but anyone any ideas? Email and FireFox worked (when installed as a temporary fix) without problems.
I reset all the security settings to default - no improvement.
The reinstall cleared the error but a friend has just called me to say the same has happened to him - might this have been caused by a dodgy windows update?
Kaspersky found nothing and a HiJackThis scan was clear.

How to use Reset Internet Explorer Settings (RIES

To use RIES in Internet Explorer 7, follow these steps:

1. Click the Tools menu, and then click Internet Options.
2. On the Advanced tab, click Reset.
3. In the Reset Internet Explorer Settings dialog box, click Reset.
4. When Internet Explorer 7 finishes restoring the default settings, click Close, and then click OK two times.
5. Close Internet Explorer 7. The changes take effect the next time that you open Internet Explorer 7.

Note for users who cannot start Internet Explorer 7 for some reason, use RIES from Internet Options in Control Panel.

Thanks Kimsland - for some reason your reply did not get the usual email advice so I did not see it.
This is a summary of the problem to date - I have not applied RIES yet but will try and will let you know.
Summary so far:
On Wednesday this week 5 machines running either XP Pro or Vista Ultimate and IE 7 all suffered the same problem with IE - it refused to open any URL. The error message was not the usual 404 and all of them were still connected to the net as emails and FTPall worked fine. Refreshing the home page in each case either produced http:/// in the address bar or a message saying the address was invalid.
All machines are running Kaspersky Internet Security and in one case an XP machine had been upgraded to SPIII and Vista upgraded to SPI. System restore made no difference.
HiJackthis run on 2 of them found no problems. By coincidence one of the Vista machines will now not talk to any other of the network computers.
I blame the updates but there is the common factor of Kaspersky. I don't think it is malware.
In each case installing FireFox produced a workaround.
Any ideas?