I wonder if you have any idea on what is wrong woth my notebook (Compaq: Presario c700) over the last week or so it has been getting very hot on the underside of it, now when I turn it on the lights are on but the fan works like it is going to start up for a few seconds then nothing happens every now and then it makes a sound like it is going to work but doesnt nothing is on the screen it is completely blank.

sounds like it has overheated, this is preventing it from turning on. It may be that a lot of dust has gathered inside the unit and the ventilation is poor. Ideally it could do with a service my disassembling the unit and cleaning it inside. Or if you are not that computer minded, then try cleaning the fan/vent section of the laptop with a vaccum or/and compressed air duster spray and see if it is any better. Hope this helps.

You might try to pull the battery of the notebook and try to turn it on. See what happens.