Don't worry, the worst that could happen by installing a wrong driver is a broken Windows install, and you can fix that by reinstalling Windows.
Anyway, this is probably a compatibility issue with the BIOS and the optical drive. There's nothing that can be done except wait for a new BIOS release to come out and hope that it fixes the problem.
Buy the full version. Most of the cheap keys are not for resale. If MS catches people selling them, they will revoke the key.
A key is for both 32 and 64-bit...
Probably a BIOS issue. I have had issues with certain Phoenix BIOSs which would refuse to POST with my external hard drive connected. My solution was to just remember to unplug the drive before booting.
While it is true that you can buy Windows 10 Pro for less with 10 Home already installed and activated, that was not his question. His question was if he can buy 8 Pro and then upgrade to 10 Pro.
Seems that it's a hardware problem. I suggest that you do a full shutdown (not a hybrid one), unplug the power cable from the PC, remove the battery (if it's a laptop), wait 10 seconds, then start it back up.
What error? Please give a detailed description or screenshot. Also, if you used the free upgrade offer to get Windows 10, you will not have a product key and you can skip prompts askig for it.