Cannot associate .dwg file to AutoCAD (Registry edit)

Well, hello everybody.
Im trying to help out my friends who owns a lil business. His problems is he cant normaly open .dwg files with AutoCAD. Let me explain it more. When he double click it there always appeaers the Open with window, and suggested are only windows media player and something with .dll . So when i tried to fix it, i tried to change it there, first of all you cant even add AutoCAD to the list ( click browse, find the program, click select, nothing happens). Therefor I tried right click properties, the file ext. is .dwg but its seen as a .dll file so i click there to change the program, well same thing again. I turn on the option to see file extension and then on double click i searched autocat, selected it and now its in the list and it opens the file. But everytime you double-click it you get the open with window. Searched through the registry and tried to delete the user choice for .dwg files and even the whole .dwg files but nothing changed. Tried some littel programs to assosiate the files to autocad, noup. Run Hijackthis, Malwarebytes, RougeKiller,tdsskiller, mgtools and SuperAntispyware , but nothing found ( except some cookies). I know I got to post the logs but I forgot to post them, and the PC is still used for his job, drawing in AutoCAD so I couldnt take it home. I will post the logs as soon as possible, but I just wanted to know if someone has a clue what and which would be the best way to fight this ?malware? .

Thanks in advance for your assitance

 

Hmmm...What would it be then? The PC will be at my place tomorrow at the end of the day. So should i post any logs and from which programs?

Thanks