Acer Aspire 1400 Shutting Off During Spyware Scans

Well, my uncles friend dropped off his laptop, and it's kinda old but has some good specs, except for the 128mb ram (which he is going to upgrade, 512mb, or something), every time i run a virus scan, adaware, or spybot, after about 20 minutes (not sure what file its accessing, as im not going to sit there for 15-30 mins to try and see it) the laptop just completely shuts off, without any warning...

Now, what is confusing is that there is no bsod, so i'm thinking hardware failure? but anytime i had hard drive failure, xp would definately bsod, maybe something so screwed in the OS? this isn't even an SP1 machine, it's got a bunch of hotfixes, but no service packs. I doubt this is a software conflict? How could that cause it to fail in such a manner, i'm kind of confused. Any ideas?

edit:
also i am running it off of AC power, and if it was the ac adapter screwing up, the battery would/should take over and the batt is charged, so im thinking it's not a power issue?

was given the ok to format it, and do a fresh install. Copied their files via safe mode with networking. Will post back if it continues to do this, he told me the last thing it did (worked fine till today) was say it had a virus, and its been doing this ever since. That's a pretty bad virus then, heres to hoping it's not hardware failure.

edit:
xp copied it's files and then the laptop shutoff during the setup, now I have mandriva 2006 installed, it installed without a hitch and has been running for 10 mins flawlessly so far, i'm going to play some lil games and install stuff, see if i can get it to shut off... otherwise im not sure why xp fails but linux runs. Anyone know how to disable acpi during windows install? i dont remember if there is an option, but thats the only thing i did differently on linux, i installed it with "noacpi", and no there isnt anything in the bios, this thing has like NOTHING you can change in there, rofl, basically the boot order, and the floppy drive.. (posting this on mandriva, too)

So i fix the mbr using a boot disk, fdisk /mbr, then proceed to try windows again, fails.... why is linux working but windows isn't? because it's not only failing, it's completely powering down, instant off.... i was on linux for 30 mins talking on msn and playing supertux... installed like 500mb of packages, so had a bunch of swap/hdd access going on, i was thinking hdd failure the whole time, but linux works, windows doesn't. This is quite the mystery? =/

edit:
just ran memtest86, went back to room to do googling, and post the above message, go back to check it out, it powered down.... WHY? Linux runs error-free? This is driving me nuts, what the hell do i tell them? It can't be hardware failure if linux runs flawless... wouldn't linux be MORE touchy than windows when it comes to hardware failure anyways? damn :S

edit2:
they gave me permission to take compressed air and poke around in the laptop, it blew out quite a lot of dust, and it SEEMS to be working, so far...