|"Drive has been formatted & was running OK until I moved it"|
What do you mean by that? Did you take the HDD out of the 3.5" bay it was mounted in & move it to a different bay?
Could it be you knocked the HSF loose why messing around inside the case & the CPU is overheating & throttling back? If not, could it be you installed some sort of crap software after you formatted & reinstalled Windows?