laptop is being really slow after new hard drive, how to diagnose it?

So one of my friend's laptop had been acting slow, and I took a look at it and I cleard out some applications but it was still going bad. it turns out the hard drive had to be replaced, so he sent it in under warranty. I reinstalled Norton 360 and Office for him, and helped him reinstall some of his games.

Then i found out it was acting slow again, and was practically unusable for gaming!

He's coming down this weekend, and I plan to take another hack at it. But I don't know what the cause would be. it's a new hard drive with a new factory image. I suspect that the new hard drive might be faulty, but I don't know how to test it. I do have some spare hard drives around that I could install, but I'd like kto know what testing processes or programs I can use to better diagnose the problem.

Any ideas? thanks.