If the PC is connected to Internet, then you can use the keyboard to navigate and reinstall the necessary driver.
Press Windows key + R then type devmgmt.msc. Using ALT + Tab switch to the Device Manager, then use Tab key to switch the items. Once you find the one with yellow (mouse, input device), press the key next to the right Control Key. It will open the usual Right Click menu. Choose Update driver using the arrows and select Windows Update, then press Enter. Let it install the drivers, attach the keyboard and that's it.
At this time, functionality should be restored. Also, remove Driver Assist and avoid installing such applications in the future.