The third will say it's the fan (when did you last clean it and the inside of your laptop to have optimal cooling?). Did you check it turns?
The fourth will say it's the PSU.
I don't think it's the hard drive. So better have it repaired by the first tech than by the second one.
But maybe you can do the cleaning yourself? See http://www.videojug.com/film/how-to-clean-a-laptop or other hits from http://www.google.com/search?q=clean+laptop (skip the parts on keyboard and screen, it's the internals you need).
I have a Dell Inspiron 6000 with Windows XP Pro. The computer won't start. When I push the on/off botton the machine will shut itself off after 10 seconds. Sometime after x numbers of attemps it will start, but after a while the machine will freeze.
Two different technicians took a look at my computer, one of them told me the problem is with the Motherboard, and the other one told me its the hard Drive.
I would like to know, what is problem, the Motherboard or the Hard Drive? Are there any books or Web Site that can help?