Asking about the slow down of the games

your RAM may be occupied by some other process.
calcel all unwanted programs in start up nad process TAB in task manager.

if this is not helping it may be some virus or some bad stuff making process slow in hidden manner.

even if this dosent help go for reformating XP freshly.

if this solution is not working dont give a rating as in-appropriate please. give the rating you feel.