tg1911 is correct. If you are unable to change your desktop background, it may not be caused by a corrupt or damaged Windows file, but rather it may still be being caused by the original infection, as it may not have been completely removed. It would help to know what your desktop is at the moment, or what it says if anything.
I would consider referring the problem to the HJT forum here at Bleeping Computer.First:
Read the Preparation Guide found HERE
. It is very important that you follow ALL of the instructions found within. Second:
Post your system information along with a brief description of the problems you are having, and your HJT log in the HJT forum found HERE
Please, after you post your HJT log DO NOT make another post in the HJT forum until it has been responded to by a member of the HJT Team. The first thing they look for, when looking for logs to reply to, is 0 replies. If you make another post there will be 1 reply. The team member glancing over the replies might think someone is already helping you out and will not respond. So, just make your post and let it sit there until a team member responds. The volunteers who work that forum are very busy, so please be patient and wait for a response. It can sometimes take a few days.
You are in good hands! Good luck!