Just turn on your PC, spam the delete key. Find something that says "restore defaults" im your BIOS, Save and Restart.
Once you get things back to ground zero, try OCing it yourself. I have had great success with my "ez button OC" software (ASUS). I have Fast and Extreme. I started with Fast, did an hour of Intel Burn Test on maximized stress, after it was stable I reset to default again, then went Extreme, restress tested. I've got a 4.5 OC with stellar temps and voltage around 1.32.
You could call the shop and tell them you to reOC your machine because you found it unstable.....or at least get your money back.