Compaq Presario 2700 bootup problem

Hi everyone, I have a Compaq Presario 2700US which is giving me a big
headache. For some reason sometimes it won't boot up. Actually it
just does not turn on the screen but won't work with an external
monitor either. The cdrom starts reading and everything but the
screen... of course it won't get to the OS start up but it does not
freeze... it powers off normally when I press the power button.

I did try the power drain following the these instructions given by HP
technitians with no luck:
1. Disconnect AC power.
2. Disconnect laptop battery.
3. Press power button in the laptop for 20 seconds (or 1 minute).
4. Connect AC power (not battery).
5. Check whether the laptop powers up.

I also tried to clearing the CMOS but nothing changed.

Any ideas?