Turn if off and on, try again. If that does not work, try hitting one of the keys to go to the BIOS setup, see if they keys work in there. If not, you need to reseat the keyboard connections to the motherboard. If they do, start the system in Safe Mode (hit F8 repeatedly after turning it on) and see if the keyboard works there. If yes, uninstall the HID devices (should be a keyboard and mouse) from device manager, reboot, wait about 10 minutes after Windows starts fully and try again.