Keyboard & Power Buttons Not Working

Hi. Got myself a used Mid 2012 MBP. decided to go for SSD upgrade after reading reviews and instructions. Install & o/s build went ok, restore from time machine went ok. Finally realised I'd done everything with touch pad. Never used keyboard. When I tried to - it won't type anything. No keys at all work. But the back light works. I flip it over and put the original disk back in. Now the power button doesn't do anything. Battery fully charged. I used the power button to turn it off to put the old disk back in. Confused & worried! Any Ideas? Thanks in advance.