Sounds like a driver issue, e.g. SATA drivers...
check to see if you have any USB devices attached, remove them ALL, then attempt to boot again...
does it boot?
have you tried to restore to a prior state, e.g. using System Restore? if not attempt that first before going on with the below instructions...
if that fails, then you may be heading towards a repair install, also called Inplace Upgrade Install, make sure that you have all drivers, the License Key, and XP boot CD at hand...
before attempting the repair install, upgrade the install CD to SP3, by using the following app on another PC, and get XP SP3 and have it ready when integrating...
nLite
once you have created a slipstreamed install CD, then read the instructions below:
How to perform an in-place upgrade (reinstallation) of Windows XP
NOTE: make back ups of your valuable DATA beforehand, any attempts at repair can run afoul and a wrong click can ruin it all...
Ben
"If it works don't fix it! If it doesn't use a sledgehammer..."
How to ask a question, when posting them to a professional forum.
Only ask questions with yes/no answers if you want "yes" or "no"