All computers produce heat, and most are cooled by air flow, hence it's important to ensure that any ventilation slots, heatsinks, etc, are kept clear, clean, and not clogged up as you have described. Assuming that there are no loose screws rattling around inside the laptop (if so, find out where they came from, and screw them back in place, otherwise they may short something), you can clean the ventilation grilles and inside the case CAREFULLY with the nozzle attachment of an ordinary domestic vacuum cleaner - hold the nozzle firmly at both ends to avoid the suction suddenly taking control.

Although laptops are usually lower powered and produce less heat than a same generation desktop, there's usually plenty of space inside the desktop, but precious little inside the laptop, hence it's particularly important to keep their ventilation slots clear. For this reason I never use mine directly on my lap, but place it on a board.

Although it sounds as though you've cracked it for now, I have a page on diagnosing hardware faults here:
www.macfh.co.uk - Diagnosing PC Hardware Faults