If you're still stuck in the BIOS and you can't get out of it through the Save & Exit section, you can likely shut down the unit by pressing and holding the power button in for at least five or six seconds. If it does not shut down, your only other option is pulling the power.
I would then first try a BIOS discharge. The instructional video is below...
If this doesn't help, I would then try reinstalling the system, which you can find
here. The system installation instruction video is also there.