Check your event viewer see if any error or warning messages are there.
Start -> Run -> eventvwr
I would prefer Windows 7 but it does use a little bit more RAM.
I haven't tried windows 8 but it is said to use lower RAM and resources.
You can try upgrading to windows 8, since there's a upgrade promotion right now for USD$39.99
Upgrade to Windows 8 - Microsoft Windows
You can run the upgrade assistant to see if your system is compatible and also to see if there's any incompatible software.
I'm not sure how the upgrade assistant will run on XP since i no longer have one to test it.