mission critical motherboard swap

[ArcanicFlame]

(in retrospect a wall of text by an idiot sorry)
so like an idiot a year ago i bought a best buy rig (i said to myself i don't need to go make a custom build online, it should be fine, the BB rig should be customizable, woops)
this rig was the gateway DX4885-ub3a i5 4440 with win 8 8gb ram 1TB HD

the mobo on this thing is so scrap i couldn't believe it
its a B85 chipset (thats a business chipset i learned) with a PROPRIETARY 12pin power connector (absolutely impossible to do anything with)

heres a link to a thread about desktops with 12 pin psu connector
bleeping computer fourms

when i bought the rig i bought a PSU and GPU the bestbuy fails said would work with the rig and obviously dont (i should've investigated compatibility >.<)

i just recently bought an Asrock z97 ATX extreme 3 mobo and an Ultra ATX Etorque X1 case so i can make this rig custom, and clutch using the PSU/GPU i bought salvaging the processor ram HD and OS (PSU thermaltake smart 750W, GPU XFX radeon HD R7770)

questions
ive never done anything like this and was wondering:
if windows (now 8.1) would recognize the new board plug and play (since the rig came with windows)
if at some point its going to ask for an activation code
if the windows product ID here in control panel-system will work for that
any other licensing issues?
any other potential software/firmware errors i'm not foreseeing?
reformat? please no
bios?

its not even paid for its on a payment plan that er well hasn't been paid.....>.>
should i return it...somehow....? i so should of returned this thing when i found this issue a week after i got it, but i didn't fully understand at the time what i was seeing....

furthermore after i saw the 12 pin psu issue i TRIED to find a 24pin to 12pin adapter but they DIDN'T EXIST (at the time anyway, i recently looked it up and found a few) i was advised at the time that even if i did find one my mobo would throttle the gpu hard

this thing should be in an office or cubicle or scraped, not in a persons home (or even home office that would be even worse) so not worth like $599 or $699? at least thats my opinion

last question, should i find the best buy guy(s) who sold it to me and throw the motherboard at them?

sorry and thank you

 

[Entomber]

1. Unlikely that your new board would work directly like you mention, I would be surprised if Windows even loaded.
2. Windows 8.1 is transferrable, but since you bought your rig from Best Buy it's likely an OEM, non-transferrable license. If you swap mobo, you will have to buy a new license.
3. Uh, if you have other motherboard-bound software like MS Office for example, those will also not work any longer.
4. You need to install all the motherboard drivers for your new motherboard before it will work properly.
5. I would recommend you reformat before trying to use your new motherboard to prevent BSODs and general unpleasantness
6. BIOS should be fine
7. Throwing a motherboard at a sales rep is both morally irresponsible and classifiable as criminal assault.

 

[USAFRet]

A preinstalled Windows 8.1 on a BestBuy box....a motherboard swap will be problematical.
The OS key is embedded in the motherboard.

What do you mean by 'mission critical'?

Scrap the bestbuy box and start fresh. With a regular Windows OS.