Viewing https pages in IE6 on XP

I am unable to view any https pages, not can I log into Passport, which I assume is https also. I have reduced the security levels to nothing and added all the sites I want access to the ‘Trusted Zone’, some using a leading asterisk others just using the address. Neither has made any difference. The other machine on my little network runs IE6 on Win 98SE and has no problem getting the pages so there does not appear to be a problem with my ISP or the internetwork path. All suggestions of blinding briliance, and, hopefully, simplicity gratefully received.