Open "Computer" or "My Computer"
Right click on the drive OR open the drive and select the folder you need to change permissions.
After you right click choose properties
Click on the security tab
Click the Edit button
Find yourself on the list (or add yourself if your not listed)
Check the Full Control box
And then click ok or apply
These steps may be different depending on your version of Windows. Might be best to google for a walkthrough with screen shots.
I agree with little_me.
Typically permissions issues are NOT an issue. Malware often causes the issue though. Even after Malware is removed this permissions issues can continue.