Can i buy a windows 8.1 re-installation disc and buy a windows 8.1 professional key from g2a and use it as a boot option??

That is all kinds of fail.

1. That doesn't look like any official 're-installation disk' I've ever seen.

2. Unless you're in a corporate environment, you almost certainly do not need Win 8.1 Pro. Zero performance difference.

3. G2A is not a legitimate source for software licenses.
Game and OS publishers have been known to retract those license keys, as they are not for resale.

I fully understand wanting to save money. But the OS is just as much a part of a new PC as is anything else. RAM/CPU/GPU/etc.

Just as you don't cheap out on those parts, don't cheap out on the OS. It's maybe 10% of the price of your new system.
Buy a valid, legal one and you'll have no problems.
 


I have read some threads and people have said keys on g2a have been fine. So all I want to know is where to find an official windows 8.1 reinstallation disc, it fails in the future I will buy a so-called legitimate one. Thanks