Perhaps the heatsink fan has quit, then computer will indeed shut down to protect the processor (CPU) If a desktop remove the side panel to see if the fan is spinning up, if a laptop feel the outlet for the air it will be on the side, back or bottom. Or if the computer stays running long enough download Speccy from Filehippo and run it to see your temps. Stay with the free version. Does the computer run for seconds, minutes or longer before shutting down?

There's nothing wrong with Vista and I think you should look a little deeper for your problem. I went with my girlfriend last week and she purchased a Toshiba Satellite laptop with Vista Home Basic Edition, 2GB RAM, 200GB Hard drive. First thing I did was remove Norton 360 through control panal/uninstall and then install AVG Anti-Virus. She wanted Photoshop installed, no problem. Next was Microsoft Office 2007, started installing and bam computer shuts down completely. I think heat, you know that they are always warm on the bottom, but no as long as there is a little clearance on the bottom for air, they'll run for hours and days on end. Decided to uninstall the trial of the preinstalled Student Microsoft Office thinking there was a conflict with the Pro version I was trying to install, went to control panel/uninstall and tried to remove the student version, bam again computer shuts down completely. Did a search on the internet for vista shuts down and the best info I could find was that it's programs running in the background causing conflicts. I remembered the Norton Removal Tool and downloaded, ran and removed all traces. Went to msconfig and took a look at the programs running at startup and thus running in the background, installed CCleaner ccsetup209_slim.exe, my preferred tool (Tools/Startup) for disabling startup and unnecessary programs from running in the background. After that Microsoft Office installed perfect and the machine has never shutdown again. Next time I have the laptop, all the bundled software is coming off, who needs it. So what I'm saying is that there is a conflict with a program that's running in the background and whatever you're doing at the time the machine shuts down. Duel boot is fine, you'll need an XP disk, $100 or less. Make a separate partition to install it on. Really very simple, less than an hour if you know what your doing. With a duel boot, you're given the choice or either booting into XP or Vista or set one as the default. I have both, doesn't matter which I use, both perform equally. First thing I'd do is remove all the bundled software that came with the machine that you don't need, especially Norton that comes preinstalled with the Toshiba Satellite and get a good Anti-Virus program. You should also have Vista Service Pack 1 installed by now.

Click Start, right click Computer, click Manage. Click + beside System Tools Click + beside Task Scheduler Click Task Scheduler Library Tasks scheduled will display to the right. When you find the offending task, right click and either delete or disable.

Thanks everyone for the best shot and trouble shootin....i have been trying to keep track of whats happening. Here's what I have noticed---Sometimes it just freezes, mouse, keyboard-does not respond to control-alt-delete at that point. Then I push button for off. 2nd-the computer goes off but the blue light is still on and can still hear running, The monitor is blank though. AGain the off button to make it go off... RAn thorough test on drive and ram-still checking out okay. Anything else I may be able to use for further testing??? I check device manager and event log. Only event log has yellow exclamations...I check out the event online but it just brings me to a generic page-then Im lost.... Will keep eye out on this-I think I read somewhere that the video card with same symptoms can cause what it does. I guess I just don't understand. It can stay on for hours and nothing happens... Thanks though for all help you have offered!!!