Inspiron 8600 random shut downs

I have an Inspiron 8600. Sometimes when I turn it on, it turns off in 1 or 2 seconds and does this sometimes 10 times in a row. Either on battery or plugged in. I had the hard drive replaced and the motherboard replaced. Sometimes it will boot up and turns off after a minute. I don't think it is a virus because it doesn't even boot up sometimes. Any thoughts.

 

How old is this computer?

 

An overheating or power issue perhaps?

When you say it turns off in 1 or 2 seconds, is that 1 or 2 seconds after pushing the power button on? Or 1 or 2 seconds after windows has started up?

Have you tried booting up in Safe Mode?

 

I don't think it's an overheating issue because he says it sometimes turns off in 1 or 2 seconds, regardless of whether or not he meant after pushing the on button or after windows boots up. That's too short of a time to overheat and get a shutdown.

He's narrowed down the possible problems a good deal. We know it's probably not his motherboard because it's been replaced. It's not his hard drive because that's been replaced as well. And he claims that the problem occurs with or without external power, so it's not the battery. I also don't think it's a Windows issue because he's not getting any Blue Screens, just shut downs.

So what other hardware components could cause this sort of behavior? Maybe his RAM has gone bad. Do laptops have a power supply similar to desktops? Maybe he is getting voltage drops.

Has anyone else heard of a problem like this with other Dells?