to be uefi correct, you must have all uefi based hardware. mobo, vid card, and a install device setup for a uefi install of OS.
New, to date machine, with w10, will most likely be a uefi pc.
W7 uefi can be done but its not a simple task as a w10 will be.
I just went thru this and struggled with a w7 install, ultimately I went w10.
w10 has many useless items eating cpu cycles and telemetricking like a ho.....ho. you will want to disable much on your gaming pc.
uefi, do you need it over legacy, NO. will it make a difference to AH, no.
Biz, get manufac software and fac set/secure erase the ssd. then see if useable. You do not format ssd's with windows really?????. very bad for them. you might see if there is a FW update for it, a FW update might reset the ssd as well. luck