Computer Infected!

My granpas computer is filled with viruses...but he has a virus that doesn let him see his desktop....and you cant install anything without it being un installed automatically anyone know how i can fix this? It would be very appreciated

He is Running
Windows XP

Please download the current version of HijackThis from HERE

• Double click and run the installer.
  
• It will install to C:\Program Files\Trend Micro\HijackThis\hijackthis.exe
  
• After installing, you should get the user agreement, press accept and Hijack This will run.
  
• Select Do a system scan and save a log file. This will open a notepad file of everything Hijack This found, copy and paste it back here.
  

Thats the thing..I cant even get to install anything because it will automatically delete it...I tried malware bytes too

Lets try this.

Please download exeHelper from one of the two links.
Link 1
Link 2

• Double-click on exeHelper.com or exeHelper.scr to run the fix.
  
• A black window should pop up, press any key to close once the fix is completed.
  
• Post the contents of log.txt (Will be created in the directory where you ran exeHelper.com)
  

Note: If the window shows a message that says "Error deleting file", please re-run the program before posting a log - and post the two logs together (they will both be in the one file).