As well as spyware, adware and virus scans...I would check your HDD for errors and defrag your drive as well if you haven't already done so.
If you don't know how, you can check your hard drive for errors by:
1. Going to My Computer.
2. Right clicking a drive and selecting Properties.
3. Clicking the Tools tab.
4. Click the Check Now button under error-checking.
The next time you start your PC, it will check that drive for errors. Do the same for any other partitions you have on your PC.
To perform a defrag:
1. Go to Control Panel.
2. Double-click on Administrative Tools.
3. Expand Storage on the left.
4. Click on Disk Defragmenter.
5. Select a volume on the right and click the Analyze button below...
Defragment the volume if the analysis informs you that the drive needs defragging.