|"I'm going to order a new gaming PC"|
How about listing the specs? Many people think they're buying a gaming PC because it's being marketed as such, but they end up with an HTPC because they don't understand the hardware specs.
And as stated above, your old HDD will not work. Windows is setup for your current hardware configuration, if you swap the drive into a different system & attempt to boot, it will detect the changes in hardware & display an error message. The best thing to do would be to back up all your important files, then wipe the HDD, repartition, reformat, & do a fresh install from scratch.