Make sure you are logged on as an Administrator account when checking your Windows/Tmp folder. If you are not and logged in as a Standard User that folder will be locked on all other User accounts but the Standard User account.
If that fails to work, download the free LOCKHUNTER utility (YOU CAN GOOGLE FOR IT!) which should tell you which app or program is holding that folder closed or locked; you can then delete it--it may require a reboot or two to accomplish a complete unlock. From there, you should be able to delete all the folders and files within your Tmp folder. If you cannot, you likely have significant windows corruption, and a full windows reinstallation with a disk wipe clean is going to be in your near future...
