XP Pro restarts after login

[lmoreau]

My Intel system board has audio built-in, but recent storm
knocked out audio. An add-in GameTheater XP sound PCI
card has been installed but not usable for over a year
(Yamaha sound driver not compatible). System was working
fine set this way for over a year.
I disabled the on-board audio in BIOS, and removed the
GameTheater XP PCI card.
When I try to start XP Pro, I get as far as the login
screen, then system will reboot.
I have tried to boot to safe mode, but the same thing
happens just after login.
For a short time, I did get system started, logged on ok
and was able to check e-mail.
However now I can not get back to the successful login
and use of XPPro.
I have tried to recreate the working setup by
reinstalling old non-functional GameTheater XP PCI card
and on-board audio settings, but that does not work either.
System restore attempts did not work when system was
able to get to the restore options, and now I can't get
that far anymore.
System constantly restarts now just after I log-in.
Also I now have the "Administrator" login option for some
reason along with my "user login" option.
Anyone else have this problem or know how to fix?