I have a Lenovo N200 laptop and have re installed Vista Home Premium recently. It now intermittently Powers off on the Vista loading screen when you turn the machine on. It also intermittently powers off when resuming from sleep mode. It does not restart, it just powers off. If it successfully loads windows it runs fine. I have re installed vista several times and ran the unit with no drivers installed, minium drivers, any driver / utility Lenovo recommends and it has not stopped the issue. I have completed RAM tests, Hard drive tests, re installed the CPU with new thermal compound and it still randomly powers off on start up. I have ran the unit with no battery installed, with no psu plugged in and it still presents with the same problem.
The thing is, if it was happening randomly when the machine was running I would have thought it was hardware related but the fact that it only happens on start up suggests it is software related. I have just enabled the boot log but typically it is loading ok at the moment.
Anyone any ideas?

If the problem occured prior to the laptops post, it would be hardware related. Because it happens after post doesn't mean it's software related,, it could still be either or.

How often does it succesfully load windows? Try booting until it loads into windows, then perform some tasks which tax the CPU, gaming or something.

It sounds like some components aren't getting the power needed to keep the laptop running, which would lead me to think it's a problem with the power supply. If you are able to keep the laptop running indeffinetly once it's booted up (shut the sleep mode option off so the laptop never shuts down) it may be an issue with where the Master Boot Record is on the hard drive.

I would also try to partition the hard drive, and install windows on a seperate part of the hard drive. If that works, chances are the problem is with the hard drive.

The machine powered off again this morning and there appears to be no boot log for the failed boot.
I have just booted from the vista installation dvd and the unit powered off just before the first installation screen (where you select language)
As far as I am aware the hard drive should not be involved at this point so I am beginning to think that there is a hardware fault, probably with the motherboard. I have left the ram testing for over four hours with no errors.

Yeah, it sounds like the power supply doesn't have enough Watts anymore to power the entire computer, or something is wrong with the motherboard.