Sounds like your doing everything right. Your OS won't load because the extra cores(core) your trying to unlock are defective.
One other option is to try unlocking only one extra core, giving you an x3. Not sure what your bios options look like, but under Cpu Core Control try selecting 3 core operation using cores0,1,2 or cores0,1,3
It's easy to unlock that combo IF the extra cores(core)are not defective....
I'd just like to add, keep in mind there is NO guarantee any of the cores you unlock will work. Alot of people seemed suprised and ask, 'what did I do wrong?' You didn't do anything wrong. The BIOS on most motherboards that support core unlocking are very simple to use.
I have this same motherboard and used the same chip, I got lucky and was able to unlock both cores and have a stable quad running at stock voltage and frequency. I would of been completely happy with it if it was a dual core as it was a huge upgrade from my 64 x2 4200 I had.
It sucks, but some of the chips do actually not have working cores, some just get lucky. It's a simple process and if you boot up and get into windows your chances are good you got a stable unlock. I burned mine in using prime 95 to check for stability and got zero errors or warnings after 5 hours. And after running this for a week straight playing video games and rendering 3D graphics that this is indeed a stable 4 core unlock that I have here.
Also, if you have 4 working cores you should see all 4 in your BIOS under CPU Core Control, should be a list of cores from 0,1,2,3. But I'm assuming core 2 and 3 will only show if they are indeed working as mine are. Otherwise you just see core 0 and 1 if you do not activate CPU Core Unlock.
When testing with Prime 95 I enabled 2 cores at a time since core 0 must always be enabled. I did this since individual core temps are not readable to check and see if any of the cores were running hotter on average than any of the other 2 cores. I have a variance of 2 to 3 degrees C on the overall cpu temp gauge, which to me isn't a concern since my old 64 x2 had one core that liked to run as high as 8C hotter than the other core for some reason.
Best bet is get a quad, they are cheap if you really need one. I didn't and my budget only allowed me to get an x2. But I got lucky and have a working quad. It's just all a crap shoot. I could buy another one for another rig and not get any cores working. I figure it's a 33% chance. since 1/3 of the time you'll get no working cores, another 1/3 get 1 working core, and 1/3 more get 2 working cores. The actual percentage maybe higher as yield rates increase on the x4's and they badge some of them as x2's to meet market demands, but there is no way to accurately measure successful unlocks without doing a lab study with at least a few dozen units on hand from different batches to see what kind of unlock rate you get.