If it is XP
pro then just go ahead and install your XP
into the drive, and it will autoload. At that point you will receive a question to either install XP
or repair an existing one. If you choose Install new, it will go thru several motions of checking HW
on Pc and eventually it will tell you that you already have Xp installed and ask you again to either install new or repair. At this point Choose repair and it will install XP
again without deleting other files.
This procedure might work on XP
home, but I don't know.
Another thing is that it might not fix your problem if your system is really messed up. It will fix all kinds of boot/load problems.
I would not start with a fresh install before running Ad-Aware and Spybot both are found here. It is highly recommended and should be run once in a while on any system, just as any good virus tool.
Also run defrag download a trial version of Excecutive Diskeeper 9, it even has a tool to speed up startup of your PC
, that must run at boot time
Also set cash not to be handle by system, but by you. Set to twice total memory, and if possible on another disk (if you have ) then the one with most activity normally.