Computer powering off - help!

Suddenly this evening my computer has started doing something very strange. While working in Word, my girlfriend highlighted a large block of text, moving the mouse down to expand the selection; at a certain point, the machine blinks off - powers down. It's repeatable: I've done it three times to try to see what was happening, but I can't figure it out... I had a similar problem with Picasa, which actually made me stop using it, though I like the program a lot: as it scanned through my images as it started up, the computer would suddenly shut down. In 25 years of working with computers, I've never seen anything like this before...

I run a 2.66gHz HP Pavilion ZD7010 laptop, with 768meg ram. I have various programs running in the background, including: NOD32, Outpost Pro, RegDefend, TrojanHunter, WindowBlinds, ObjectDock, WindowFX, TopDesk, Google Desktop, AdMuncher, The Bat!, CalendarScope, WinPatrol, ProcessTamer, Konfabulator, MS Antispyware.

Has anyone ever seen something like this? Do any of the programs listed above suggest areas for me to investigate?

Thanks for any help...

 

What is the make and model of the graphics cards and the power supply?

 

It's an nVidia GeForce FX Go5600 card, with 64mb graphics memory, and the power supply is a standard HP AC adapter - it says on the body that it is a series PPP0168, in case that means anything.

Since posting, I have downloaded and installed the recommended video drivers from the HP site - I think I was using newer versions previously - and have just restarted. When I've pressed 'submit reply', I will open Word again to see if it's continuing to do the same thing.

 

Nope, did the same thing, and with a different document too. I'm scratching my head here... Anybody?

 

Okay, I'm onto something here... I've taken out the 512mb memory stick that I bought a few months back, and replaced it with the original HP 256mb stick, and the problem doesn't happen. What I realised was that it was managing to select about 4 screens worth of text before switching off - so I tested it with a PDF document, and lo! it did the same thing. I'm just downloading Picasa again to try that and see if it works... Can anyone advise me on how to test the memory for physical or other errors, or is there a chance I can just wipe it down, put it back and it'll work properly? (Naive about memory, it seems.) .... [time passes] ... Picasa works fine with the old memory restored! So, looks like a memory problem - can anyone advise how to test the memory?

 

There are some physical testing tools, I would have to look them up. The simplest thing to do is disable quick boot in your BIOS and allow the system to do it's own diagnostic. Personally I hate quick boot. Why boot a system and ignore a potential problem? Just hit escape if you want to bypass the diagnostic.