Computer Randomly Shuts Down! HELP ME PLEASE

My computer keeps randomly shutting down. I have a HP laptop with Windows Vista.
It just started yesterday! It randomly shuts itself down. I have an HP Laptop with Vista. The motherboard was replaced last year, (defective straight from factory). Everything else is good in it. I can't keep it on long enough to do ANYTHING with it, updating or anything. I can't keep it on long enough to run my anti-virus scan to see if this was a virus. Then once I turn it back on I get that, your computer unexpectently shut down, check the disk drives, etc. HELP ME PLEASE!!! I need it fixed by Monday morning (today is Saturday morning here). I have to use my laptop at work Monday, but right now I don't see that happening. I'm fully prepared to do a full system restore if that'll fix the issue. I HAD restore points, but something happened and now they are gone (gotta run the anti-virus scan once the computer stays on, think that might be a virus). Its not overheating, its not dusty.

PLEASE HELP ME! My computer is only 2 years old, its gotta a lotta life ahead of it..

I think your computer is overheating, you can download HW Monitor and check the temperatures and if they are very high open it up & clean, get a can of compressed air and clean the fan and ventilations.
You can download HWMonitor from here:Download HWMonitor 1.15.0 - A hardware monitoring software that will read the system's main health sensors - Softpedia

Welcome tiggerspiglet

Turn off the computer, then during boot hit f8 (safe mode). If it works in that condition, follow these instructions.

View and try this video courtesy of another member Jfar. I will get the video.
http://video.about.com/pcsupport/Fix-Laptop-PC.htm

Make a virus scan.
Download and run malwarebytes.

How to troubleshoot a problem by performing a clean boot in Windows Vista or in Windows 7

We will try to help

Here is the link for malwarebytes. I and many others use it, its fantastic. Even if it does not solve this problem, it should be used once a week to avoid future problems. Us it in addition to your A/V

Malwarebytes.org