Quote Originally Posted by broomdodger View Post
If you have a wireless keyboard...
find a WIRED keyboard for the following.

Unplug ALL peripherals
Plug in ONLY a wired keyboard

Reset SMC for iMac
Shut the iMac down
Unplug the iMac from power
Wait 15 seconds with the iMac unplugged
Plug the power cord in and wait 5 seconds

Press the power button
Immediately hold down the COMMAND and letter S keys
Until you see a black screen with white letters

Did you get to a black screen with white text?

Do you still see vertical lines?
If yes, then it is a bad GPU.

Force quit the iMac:
Hold the power button until iMac shut down.
I've now got a USB keyboard on order which should arrive relatively soon hopefully. I've already tried resetting the SMC but haven't been able to boot into single user mode as you have suggested due to the current keyboard situation. A solution I have found online which I am going to try if all else fails and I am able to boot into Single User mode is to bypass the GPU all together as mentioned in the link here. Once again, I will report back onto the forum with any developments to the situation.

Thank you for your suggestions.