When you go to event viewer, click on system and look for errors and question marks.
Do a thorough virus and spyware/rootkit check of all hard drives.
Go to services (services.msc in run) turn off Indexing.
Go to control panel, system, advanced, performance, turn off cache for each drive.
Reboot then delete pagefile.sys on every drive.
Some applications will complain, you can turn cache back on after cleaning system thoroughly.