I own the GL62M 7RE model and I've been having this issue for months now. I tried updating the BIOS, EC and the Chipset and it worked fine for a few hours. But now my keys that i've had issues with do not work at all. Lots of people have been having the same issue as me with the embedded keyboard specifically. USB keyboards work fine and I don't have issue with the keyboard in the BIOS, so I wonder if it's a faulty driver or some sort of software bug from Steelseries. There is no physical damage that I know of to the keyboard.
I'd prefer not to RMA my laptop because I don't have this laptop registered because I got it as a gift nearly two years ago.
Reboot the computer (without reinstalling the driver).
When it restarts, it should reinstall the driver on its own.
If this doesn't help, and the keyboard works fine in BIOS, plus the external works fine, then I would try going into "Safe Mode" and see if it works in there. If it does, then your problem may not be a driver, but something else on the device. Bad program, virus, malware, etc.