Are you sure the MBAM.exe wasn't deleted by the malware? See if this post helps. Download and save the "randomized renamed mbam.exe" and place it in the Program Files\Malwarebytes' Anti-Malware folder, as instructed.
It's quite possible you may run into other issues, but it's a place to start.
Best of luck..
Run XP for Windows...downloading Malware free edition and after completing "successfully" it can not find mbam.exe