Can’t access HTTPS pages on IE6 and XP

I have a client that runs a Dell with Windows XP and IE6 installed. All has been well until last week. All of a sudden they are unable to view any web page that has a HTTPS page. As well when I try to access Windows update site I’m informed that theSECURITY level of the browser is set to high, yet I have gone in and change those settings to the minimum with no change. I installed Netscape to have an alternative and that browser will access HTTPS pages. I am stumped. Anybody have simalar problems / fix?