Recently I had the job of fixing a Compaq F700 that overheated and shut off after about 15 minutes of operation. Needless to say the cooling fan was completely clogged with dust as can be seen in the picture below.
There is another screw that can only be reached from above,
once the CD ROM is removed. There is a hole now available that goes
down through where the CD drive had been to access a hidden screw down
below. You have to remove the screen and all the usual screws to
finally get the top cover off the laptop. Once you remove the main
board the cooling fan screws are hidden under some black sticky
plastic. They are extra small and hard to remove.