Sony Vaio laptop vgn-fs640-w problems

Question

very unusual problem....laptop will not boot upwhen you power it on the dvd drives powers up, hard drive powers up and the lights all light up but the fan does not turn on and the screen does not turn on..........i took the laptop apart and looked for anything that looked bad..didnt see anything i then powered it up and the computer turned on and started to boot up fine and then the screen just went black and the hard drive was still on and dvd drive still on...fan was still on...i kept messing with it and now all i can get is the screen to come on somethimes but not to boot it just shows the sony splash screen and thats it...could this be a bad processor??? prior to this the laptop would work ok and then freeze and shut down........it got more frequent and now i can only get it to boot up maybe 1 time out of 50 times.if i tap hard on the bottom of the motherboard i can get the screen to come on but it does not boot just goes to the sony splash screen and freezes there...and the fan does not power on.......does the cpu tell the fan to power on..or should the fan come on as soon as laptop is turned on....when i can get it to boot it seems like the fan comes on once the pc starts botting up past the splash screen...it uses a pentium centrino 1.6 ghz