Ooh man. That sounds really crappy.
Okay. I've just logged in onto my Gmail account using the Mozilla Firefox browser, and everything works fine. I can see my messages very clearly, and everything seems to work as per normal. I don't have a Hotmail account, but I do have a Passport, and so far I don't have any problems logging onto MSN.com, either. So as far as I can see, it most probably isn't an error on Gmail or Hotmail's side.
You said that your HijackThis log has already been reviewed by staff of the site, and that your computer is clean, so it shouldn't be a malware problem, either. And if you have done everything that the other members have suggested you to on this thread (disabling of firewall, et cetera), then it couldn't be an issue with too-high security either. At this point I myself really have no idea just what problem could it be, since your computer seems to be working perfectly okay otherwise.
I don't really know whether this would work or not but it might just be worth a try. There's a program integrated into Windows XP called System Restore - it, as the name suggests, restores your computer back to its original state on a certain date. Since your problem began cropping up on Tuesday, restore it back to a few days before that like say, Sunday or Saturday. If there aren't any system restore points created on suitable dates, you can try restoring it to the last available date - although that can be pretty inconvenient, especially if say you've got some important programs downloaded a while ago or significant changes that made to your system, since you'll have to redo them again. However, like what BKO
suggested, it could very well be a new program installed a while ago that only recently began interfering with the loading, and if that's so, restoring your system might very well be the solution to that problem. Also keep in mind that you can always undo the system restore if you want to, so there really isn't any loss in trying that out.
Hope that helps - personally, I've never encountered this sort of problem before and I'm quite unsure as to what to do about this either...