Yep that can be an issue. Try using the arrow keys to select you OS's hard drive hit enter and continue tapping the F8 key. Don't drum it just tap it intermittently and see if you can get to the boot options to select safemode with networking. MalwareBytes is not an issue, I've never seen it produce any similar issues as you are having. You may want to consider at some point in the future installing MSE just for peace of mind. Run the update feature and perform a full scan. It's a reasonably decent product, with a small footprint overall, easy on system resources and doesn't usually cause any networking issues as a rule.