XP won't boot

[Shopper]

I'm posting from old HD with win98. I have a problem and can't get XP to
boot. This happened very suddenly, without warning. I had a program
(Snag-it) which I wanted to run and got an error message so I thought I
would re-boot. I shut down normally and now XP comes up with this horrible
screen giving me options to select a most recent successful boot or safe
boot etc. None will complete. Windows simply goes into continuous re-boot
attempts loop no matter which option is selected. It goes as far as the
Windows XP screen and then reverts back to a restart. The proper size HD and
amount of memory appears on the initial boot screen so I think the HD is
still good. I have no recovery floopy disc unfortunately but nothing very
important will be lost if I fail to get this running. Only recent e-mails
etc. All important files are backed to external drive.

Any hints on where to go from here? Is it possible I picked up a virus? How
I don't know because I haven't d/l anything recently and haven't received
any file attachments that got through in the past several days.

Thanks