Re-Install

My old pc, a 1.6Ghz system is starting to let me down, I'm hoping it's just because it's old and XP has been on it for years and windows may have become corrupted. I really would like to run SH3 on it for a few more years if possible. My big problem with this version of XP is microsoft will not validate it because it's an OEM version.

Question, is it possible to re-write xp over the top of the system already in place without re-formating the hard drive, the idea being if the old files are corrupted a re-write from the original CD may be the cure.

thanks