Do I have a virus? XP login issue

OK, so I have a problem I cannot solve. Here is the turn of events:

* I have Windows XP SP2, Norton Antivirus 2005.
* I accidentally im so ashamed opened up a file that I believe may have
contained a virus. Norton did not catch the executable, nor warn me of an
impending problem, so the thought that this executable contained a virus is
theory.
* The executable did nothing noticable.
* When I restarted my computer, however, XP took a bit longer than normal
to boot. When it did come up, the desktop wallpaper showed, but no icons. I
could not Ctrl-Alt-Del either. Then, after about 1 minute, I was reverted
back to the XP login screen. When I clicked on my account to see if it would
log me in, it tried to load my settings, and I was quickly (less than half a
second) forced back to the login screen.
* Any attempts to reboot after this were met with the same issue.
* Windows safe mode showed the same results. No ability to gain control of
the desktop.
* At this point, I could not execute System Restore, so I got out my trusty
XP disk and did a Windows repair.
* The windows repair worked! I was able to access all my files, and
everything seemed normal, UNTIL...
* I reboot the system. Once XP comes back up after the second reboot, the
same problem detailed above applies.
* Ive tried rebuilding XP then running a full system scan to find no
inherent virus. I cannot upgrade to SP2 due to the system requiring a reboot
to complete.

I know thats long-winded, but I'm at the end of my rope. I'm about to go
through a complte data migration and full re-install if I can't figure
something out soon. Any ideas??

Thank you much -
Russell