Ok...
I took it back to the shop.
They were able to make it work by changing the hard drive
According to them all I gotta do is format my HD and re-install everything.
Aaaaaaaaand somehow I changed my HD's default set-up (may be changed it from SATA to RAID-0 in BIOS) which I gotta re-roll to.
Will give an update as soon as I can get somewhere with it.