Games Slowing Down - Help!

Guys my mate is having a bit of a problem with his machine and I can figure it out.

He has 4 GB DDR2 800, GTX 280, Core 2 Q6600, Vista Ultimate 32

He has recently formatted his machine and installed Far Cry 2, COD 5, and DOW - SS.

His games seem to slow down and lag as if playing an MMO on a poor connection.

He previously had no problems running these games and it is only recent that this problem has occured.

In Dawn Of War (A relatively old game) his sound starts to get choppy and the game slows down as if his CPU is under a crazily heavy load.

I checked his processes, and he has nothing out of the ordinary - just a few running.

He is running Norton - but has had no issues with it in the past.

He has no downloads, and no scans running at the time of the incidents.

He has the latest drivers for his GPU and latest updates for his OS.

Any ideas? I'm out Quick responses will be greatly appreciated

Just ran NV Monitor again and it says HDD is chugging at 100% - wierd. Ideas?

Well if it is a new format of Vista, it will take a few days to fully index and set up how Vista wants to be set up. Trying to play a game with 100% HDD use will slow any machine and any game down.