If the system isn't booting to a floppy disk or a CDROM the problem isn't windows itself it's a problem with your BIOS setup.
Load "setup" at the systems initial splash screen and verify that the hard drive(s) and CDROM are being correctly initialized and
are set to the correct the correct types. You'll also have to verify that the correct drive is being booted and the boot sequence
has either floppy drive or CDROM (or both) are booted before the hard drive.
Frankly I wouldn't be surprised if you find the motherboard is toast but it sounds like CMOS lost power and reset to some default
setup booting to a non existent drive or one which has the wrong drive type for your hard drive. It should be set to Large or LBA
but you will likely find it listed as normal. the CDROM drive should be set to normal for it's type.
If you do get the system to boot to floppy or CDROM try restarting windows first (the changes in BIOS may have made the system
bootable). If you still have a problem with boot.ini the file has likely been corrupted and you should boot to the windows XP CD
and run the recovery console to use the command fixboot to attempt to fix the windows startup files.
http://support.microsoft.com/default.aspx?scid=kb;EN-US;314058
If that fails you can try using a repair install as described on this page
http://www.webtree.ca/windowsxp/repair_xp.htm
--
Dale Beaudette
Associate Expert
The Expert Zone
http://www.microsoft.com/windowsxp/expertzone/default.asp