is there anything important on the HDD? There's a few ways to backup data from the BIOS if you absolutely have to, then follow with a clean install. Only advice I can give if you've tried the simplest things already.
Have you made sure your mouse/keyboard are plugged into usb 2.0 slots and not 3.0?
Is this a new machine or did the computer used to work properly?
If it used to work, like the above poster said, try booting into safe mode with networking and re-installing your peripheral drivers.