you can do the following to replace missing or corrupt system files.
Go to start click once, then select run, then type in cmd, when the black
screen pops up, enter sfc /f
Include the space, you may need the original xp install disc.
also to reinstall the games, go to the control panel select the add/remove
programs
then select the windows files and select the proper programs you want
installed, ensure they are checked. if you remove the check it will be
uninstalled.
you are going to find you will need the install cd for lots of things.
Check and see if you have a hidden partition for a system restore, to as new
condition, if so you can try this, but be aware you will lose any new data
added to the system since you got it home, ie pictures/personal data/e-mail
etc..
I would suggest you find a way to back those up, before you perform a restore.