You might have the best luck if you use safe mode to  run Malwarebytes. 

To access safe mode turn off the computer.

Now press the button to start the computer and press F8 (a function key on the top of your keyboard) about every 3/4 of  a second.

You should get a black and white screen listing safe mode, safe mode with networking and other options.
Choose safe mode with networking by using your cursor keys (the ones with arrows) to move to the selection, press enter.
The safe mode screen will not look like your normal desktop as it will probably be at low resolution.  Don't worry, when you boot back to normal everything will be the right size.
Now find Malwarebytes and run it.
When it's done, follow instructions and reboot.  Safe mode start screen will look like below;