One of my coworkers is using a Dell laptop with Vista home premium (x86). She was telling about this weird problem where the computer would sometimes load Vista all the way to the desktop. But other times you'd see the DELL logo startup and then the Vista "loading bar" would appear like its going to actually load the OS but then you just get a blank screen after that. It essentially hangs somewhere when trying to load the OS.

At work me and another PC guru tried to reproduce the problem but it was very random.

The woman who owns the PC took it to Best Buy and had the Geek Squad look at it earlier. They said it was free of spyware/viruses/spam etc. I inspected the PC myself both in the BIOS settings and the few times it loaded into the desktop. There were no anomalies that I noticed.

So, what could this be? Bad PSU? Vista needs to be reinstalled?

Opinions welcome!