I am going to play the devils advocate here but do you have pets in the house, namely cats?
Or do you run your Laptop on your bed, with no hard surface (I.E. LARGE book or piece of plywood) beneath it?
Do you eat above or near your Laptop?
Are you running a good Anti-Virus program on Vista ( Vista = memories of windoz Millennium.Edition. build a piece of crap and force it on all the masses and dump it in 2 years or less).
Why am I asking ....(A). Sounds like a cooling issue, cat fur built up in internal fan...
(B). Cooling issue, you are running it on soft surface and it simple cannot pass enough CFM of air across processor to cool it.. It cannot breath when running on soft surfaces, plus it will pick up dust there also...
(C). You have dropped something down threw the top vent that is in the way of rotation of the fan.... Fan cannot spin system will lock first and then just shut off to preserve itself.
Solution for all 3 problems above, find someone that has a CHEAP Leaf blower, WHY CHEAP, you need one that produces less than 100 MPH Peek power, (from tube or front of blower, also an old Vacuum that has a blower on it works very well).
Sit the Laptop on a HARD CLEAN surface, Ask someone to hold it for you if available. Blow air ( and all of the people that will say go by canned air, that does NOT produce enough air flow to help...) into the bottom port (VENT intake) on the bottom of the laptop ( Laptop is OFF when you do this )
DO NOT get the tip of what ever blower you are using right into the vent.
DO NOT blow for more than a few seconds at a time, like 2 or 3 seconds only, any longer and the fan will burn up the bearings/ frictionless pads/ hydraulic fluid.
Switch Back and forth blowing in one side and into the back and into the bottom, do each side repeatedly.
I have worked on thousands, of laptops dating back to 2001 and this is one of the most common issues I have seen.
Now about the anti virus, If you got a root kit and you are NOT wiping ( Means formatting the entire disk, NOT Quick format, complete data destruction for ALL data on that disk ) and reinstalling Vista then it will just come back each and every install...
Rant for the week complete, Thank you all for your time...