For testing purposes, it's best to install Windows "clean".
This is, basically, installing it the way that Microsoft intended (using drivers from Windows Update).
Backup all your data.
This will wipe your hard drive of everything, so anything that you want to keep will need to be saved elsewhere.
Connect the system to the internet
Use DBAN (
DBAN Download | Darik's Boot And Nuke ) or KillDisk (
Active@ Kill Disk. Hard Drives Eraser. Free Download. ) to wipe the drive
Install Windows by booting from the installation DVD
Visit Windows Update and get all updates
Visit Windows Update and get Service Pack 1 (usually under Important Updates)
Visit Windows Update and get any other available updates
Check Device Manager for any unknown/disabled devices - if there are unknown/disabled devices, fix them with the latest drivers from the device manufacturer's website (not the PC Manufacturer)
Download, install, and update a free antivirus so you don't get infected while testing (
Free AntiVirus ).
If the problems persist, then the problem is most likely with your hardware.
CAVEAT: If you have an Asus motherboard, check the date on the C:\Windows\System32\driver\ASACPI.sys file. 2004/2005 is a problem, 2009,2010 is OK.