Open a command prompt, type: sfc /scannow
Let that finish, then go to bleepingcomputer.com and download TDSSkiller, adwcleaner, combfix, and windows repair from tweaking.com
Run those in the order I listed.
***Windows Repair - Go to start repairs, select everything (for simplicity) unless you have Windows 7 (then uncheck the Windows 8 fixes) and hit start.
Then see if you can install any AV software or get malwarebytes to run.