1) Laptop needs to be kept clean inside. If you, or a tech has never opened the laptop to clean it, this is the problem.
The hardware components inside are cooled by air.
Dust, dirt, hair, food crumbs, lint, you name it, can clog the cooling components inside, and make the laptop overheat.
The Processor, and the graphics chipset give off the most heat.
If a Processor overheats it turns off. (BIOS turns it off actually)
Shooting air from the outside is a bandaid approach at best. The problem will return.http://support.dell.com/support/edocs/systems/plav/sm/index.htm
Removing and Replacing Parts
(Buy and wear an ESD wrist strap. Cost average is $3 to $6.
Connect the alligator clip to a good ground source)
2) Bad Power MOSFET/s.
Example using HP Pavilion dv6000 series, and Pavilion dv9000 series Notebook PC's,http://mayohardware.blogspot.com/2010/04/important-parts-on-dv6000-and-dv9000.html
Also look at the second photo down. Note the small rectangular shaped object to the left of AO4407 circled in Yellow.
Has a dark wide band in the middle.
This is a Ceramic Capacitor.
There is one above it, one above that one, and one to the right of the top one. Just a few that size.
These go bad also.
Visual signs of bad ceramic capacitors, and power MOSFETs, will be blackened, or blistered, or bubbled.
Cost example of a Fairchild Semiconductor - FDS6679 - Power MOSFET,http://www.mouser.com/Search/Refine.aspx?Keyword=FDS6679
One dollar and one penny.
Average example of ceramic capacitors,http://www.mouser.com/Passive-Components/Capacitors/Ceramic-Capacitors/Multilayer-Ceramic-Capacitors-MLCC-SMD-SMT/_/N-b2cj?P=1z0wrkgZ1z0vhw8
You can use a low wattage soldering iron with the beveled tip, and not have to use a Soldering Station,http://www.youtube.com/watch?v=5uiroWBkdFY
Or hot air,http://www.youtube.com/watch?v=MqivHi7Qjvk