Laptop lockup

[Calaber]

Ok, here's a problem for the laptop gurus.

My Asus laptop has carked it. I suspected the hard drive, so swapped a working 160gb h/d from my son's similar laptop and it worked fine for a full day. During that time, I spent hours cleaning and defragging his h/d, deleting crap programs that he had installed but no longer used, and installing my printer drivers, Avast Anti-Virus (full edition - paid for and licensed) and AVS (also licensed and paid for).

The laptop was left on overnight and the next morning, the screen was dead. I was advised how to kick start the thing and followed the battery out/power lead out/hold power button down for 15 secs/power lead back in/battery back in. The laptop went through its start up until it came to the screen which gave me the option of starting windows normally or seeking the self diagnostic process, which I chose.

The laptop started the diagnostic, but locked as per the photos below. That is, it went through the diagnostic process until it got to the stage shown in the pics, then stopped going any further. After a while, the screen went blank again. The h/d light flickers while the diagnostic is working, but stops flashing when it gets to this stage shown below. I don't think the h/d has died this time, but can anybody suggest what the problem might be? Obviously, the screen and video card should be ok as I am able to see the process working until it locks.

The laptop runs Vista home premium and only has 2gd of RAM. 1.6 ghz CPU.

Any suggestions?