Oh, and replace your HDD under warranty, it probably shouldn't be taking that long to format - after checking all your cables and maybe try a known recently good PSU, just in case.
The hardware will keep retrying a sector, so the software can't always tell if it should mark an entire cluster as bad or not. Either way it sounds like your HDD is defective.
ie: Good media + Good RAM + Defective HDD = corrupt files.
The data gets copied to RAM before it hits the HDD though, so you never really can tell...