Should be in your manual, yep!
As far as questions...
You bunked this... but should check it regardless. You did move the HDD so possibly a bump may have messed the drive up...
Another thing you can try is running a benchmark against the drive like HDTune, HDTach, to see if its performing as it should. Also try the seagate tools diagnostic.
As far as questions...
Did you install in AHCI mode? If not: http://www.tenforums.com/drivers-har...tallation.html
Does it do this at stock speed as well?
As far as the unpluging hardware/USB thing, clearly you will still have the problem when you plug it back in. The point is to find out WHAT is at fault. If it changes with out USB devices plugged in, we know it either a driver issue there (did you install your USB drivers?) or hardware not playing nice. I have had this happen on some systems with USB sticks plugged in... may not be your issue, but had it happen before.
You bunked this... but should check it regardless. You did move the HDD so possibly a bump may have messed the drive up...
If it is used hard drive I would certainly check the smart drive data with Crystaldiskinfo.
I would also run: the sfc /scannow from a command prompt with admin privileges and then run chkdsk /f /r (also with admin privileges) from command prompt. The latter command can take several hours to complete and seems to get stuck on 10-11% forever but its not stuck.
Another thing you can try is running a benchmark against the drive like HDTune, HDTach, to see if its performing as it should. Also try the seagate tools diagnostic.