Hmm! Interesting error!
It's
NEVER a good idea to turn off (or reset) a computer while it's running a disk checking program - very easy to end up with a heap of corrupt files. Try booting the system into safe mode (tap F8 after POST to get a boot menu). If it fires up then do a system restore back to before you ran the scans. If it doesn't then you can use the same boot menu (F8) to select "Last Known Good Configuration".
If none of the above works then get your XP CD out and boot the system from it. Follow the instructions
here to do a repair of XP. Before you do that. tho', it would be a good idea to do a scan of the hard disk for errors. Boot from the CD and press "R" at the first screen it stops at. Select the XP you want to log into (usually 1) and enter your password (or just press enter if you don't have one). At the prompt type (without quotes) "chkdsk /r" and press enter. Once it completes (and it may take a while) reboot the system normally and see if it will now fire up. If not then do the repair install.