Doesn't really sound like this problem but you can try this if you are stuck for any other answer.
You can boot to the XP cd and when you see the Welcome to setup press the letter R
You will get a dos prompt
Then type "chkdsk /p" without the quotes and hit enter
When that is done type "fixboot" and hit enter
"Y" and enter at the prompt
Then type "exit" and hit enter
The system will now reboot into Windows
If for some reason that don't work for you, you can boot to the recovery console like above and...
Type "chkdsk /r" then enter
When done type "exit" and hit enter.
This will take longer, but the system should boot back into Windows.