We need clear information.
You have a version of XP that was working good on this Laptop?
Next you went to install Windows 7 over it and it failed?
Did you use the recommended method of doing a fresh install of putting Windows XP onto a laptop that had Vista or Win7.
Microsoft and this forum have warned users that an install of Windos XP on a Hard Drive that had Vista or Win 7 will fail. Unless you follow the specific instructions.
Here are the general instructions that should work in most cases. (Some details will not apply.)
http://support.microsoft.com/kb/313348If you did that and it failed, please note the error, if any, and come back here.