Startup Problems, WinXP-Home, SP2

I have a "generic" computer that was built by a local computer shop. It has
an Aseus motherboard with the nVidia integrated devices. I've got an AMD
1.80 Ghz processor, 512 MB RAM and of course the usual hard drives,
CD-BURNER, and DVD-ROM drive. I also have a ZIP drive connected via USB. The
computer was two years old in September. It originally had WinXP-Home, SP1.

Three weeks ago today my computer started doing something VERY strange. My
wife powered it on of a morning like she always does (we normally shut the
computer down at night). During boot-up, it hung with the opening Windows XP
screen...the screen where the little bar is moving across the screen. So, I
had my wife to boot into Safe Mode...and we ran Adaware, which found a few
items...took care of those...and the computer rebooted. I was relieved...

It lasted a day...2 days later...the problem happened again. This time, I
ran the WinXP Repair option. Again...the problem went away...and lasted 2
days. This same thing happened again...no kind of error message...no clue as
to the problem. It just hangs on that opening screen. I decided in this case
to apply SP2 and see what that would do. Well...it didn't help at all. It
hung in the same spot immediately after installing SP2.

At this point, I decided it was time to clean the hard drive off, do a fresh
install of Windows and also install the latest nVidia drivers. I decided I
would also install SP2. I did all of that just over 2 weeks ago. The
computer has been working great...everything seeming to be fine. No errors
with any of the devices...just nice bootups and shutdowns, etc., until...

This morning...out of the clear blue...the problem was back. The exact same
thing happened! No errors...no clues...no bootup. It booted up once and I
installed an update to my virus program and decided to reboot...and that is
where it hung.

This time...I decided to boot into the Safe Mode...uninstall the nVidia
package of drivers...and reinstall the nVidia package. This seemed to get it
back to a working state (I booted it up 2 or 3 times without problems).
However, I'm very frustrated and discouraged...and clueless on how to fix
this so it won't happen again.

Needless to say...the computer always shuts down fine...no kinds of errors
or hang ups that we know of. Even trying to boot into the "last good
configuration" mode always fails.

Any thoughts or ideas? Please e-mail me at mjwsjw@myway.com.

Thanks in advance.