Alright you tried a system restore with no luck. You updated your chipset drivers with no luck. Have you scanned for viruses and spyware? Check out our guide and go through that.
Other than that i would say check for updates to XP. SP3 is out. It is not as bad as people say either. What software do you have set to run on boot?
Check that and make sure you dont ahve anyting in there that you dont know about or want to boot up. Also while there check under the services tab. Check the box at the bottom to hide the Microsoft services and see what is left. Remove any that you do not need on a constant basis. Things like Adobe have several services that start for no reason.
If that still doesnt get you anywhere. Try a inplace upgrade also known as a Repair install.
How to Perform a Windows XP Repair Install