Dell laptop motherboard repair

[RonTwit]

I bought a used Dell Dimension 750 laptop last year at a "Super Computer Sale". After getting it home, I noticed the USB port was broken (although everything else worked fine). I bought a used "as is" motherboard off e-Bay, but it apparently was dead. I tried swapping the power converter board from the original board to the e-Bay board, with no success. Since doing that, I put everything back together as originally purchased, and now the computer won't boot! All I get is the hard drive light glows for 3 seconds then turns off (nothing spins up, no noise, just the light).

Being a glutton for punishment, I bought another used board off e-Bay, but I get the same behavior (drive light for a couple seconds).

Any chance I can get one of these three boards to boot up again? What might have gone wrong with my original one that it no longer boots? I was always careful to keep myself grounded.

[Bryce W]

It sounds like you arent connecting it back together correctly, dead CPU or a dead motherboard. Since the fans arent spinning up I would look how they are connected. If they are connected directly to a molex connector (about an inch wide with 4 pins that comes out of the power supply) then you can assume its going to be a power issue.
If your fans connect to the motherboard you might have a dead motherboard on your hands.

Let us know how the fans are connected to help us further pin-point the problem.

[RonTwit]

There is only one fan on the laptop, and it connects to the motherboard with a very small 2- or 3-wire connector about 1/4" wide.
One correction to my original post: I said that the hard drive light comes on for a few seconds. After looking more closely at the laptop, it's the power light that turns on briefly. The hard drive light does not come on at all. (The other light on the unit is the battery charging light, which is always on whenever the power cord is attached and the battery is installed.)
One more thing I tried, to eliminate the possibility of a piece of hardware causing the trouble, is removing the hard drive, the CD-ROM drive, and the battery, (and with no card in the PCMCIA slot) and just trying to boot up with the power cord attache; I got the same result, i.e., the power light turned on for a couple of seconds then turned off.

[Bryce W]

To ask the obvious, is the power adapter and battery known to be good? Perhaps you should re-test them? If they had problems it would explain why all three motherboards and the original ones have the same behavior.