HTTPS don’t work in IE

Hi folks.
This problem is very strange, a friend of mine called me yesterday saying her machine was full of spy stuff, so I went there to fix it, and I did all but can't solve the problem where in Internet Explorer it can't deal with any HTTPS URL, it says 'page cannot be displayed', so she can't login or buy stuff online over a secure channel.

This only happens in IE, I installed Firefox and it works, what could be the problem?

Thanks.

what version of IE are they using?

can always try the latest build, has it had a virus check, coz there maybe a virs that attacks IE.

but then the simple thing is it is IE. lol. never ask anything of IE, the likly hood is it wont work

dpyers:

Yep, will check if the certs lists are there, didn't though of that.

dj air:

I think it's IE 6 since she has XP with all updates on it.

huwnet:

No proxy at all, she only has an un-activated Norton Anti-Virus and WIndows Firewall.

Still don't know what could be causing it, I'm trying to avoid having to re-install Windows just because of that. Googling around din't shed any light either.