1..What i would try first is boot into Safe Mode (f8) and see if problem is present there as well.İf everything works fine in Safe Mode then some third party services are probably causing the problems.
2.. a clean boot to troubleshoot the problem http://support.microsoft.com/kb/929135
3..How much RAM have you got? İf there's enough then next step 4.. would be a scan with http://www.eset.com/us/online-scanner/
(best to access the site with İE)run a scan,checkmark all appropriate boxes,including 'check archives,
click on advanced settings and checkmark ''scan for potentialy unsafe apps'
disable your antivirus just before you run Start
and re-enable it afterwards.The scanner will give you the option to delete anything it finds at the end.
Please do that and if after a cleaning of your disk and a reboot,the problem persists,please let us know the results.
İf no malware is found we'll have to do chkdsk next.
P.S İf malware is found please also go to Start>Run type prefetch click ok and delete everything on that page,then empty Recycle bin and reboot.
Edited by Julia G, 12 December 2012 - 09:19 AM.