Why does this brand new HP a1440n desktop keep freezing?

My boyfriend has a brand new HP a1440n desktop PC. It freezes constantly. It froze when he started it for the first time. It freezes while on safe websites, while palying Quake, while playing World of Warcraft, no matter what he's doing. He has up to date virus protection, and has not downloaded anything sketchy. Since the PC is under warranty, he has already had the hard drive replaced, but it still freezes. The PC has an Intel Viiv Processeor and an nVidia graphics card. Does anyone know what he problem could be?