Computer starts up when connecting AC power

We have an old compaq that we are trying to use in our lab here. Problem is, as soon as we connect the AC power cable to the back of the desktop, it immediately starts doing a boot.

There are no settings in the BIOS that allow this function, and we do not have a LAN cable attached so boot on LAN is not the issue.

One thing though, when we tried to install Windows from two different disks, right when it gets to the part on the blue screen setup window that says "Setup is starting Windows" boom, all power shuts down and the computer stays off. Not even the power switch brings it back up. We have to unplug it and plug it in again. Also, there is a faint alarm going off. Not beeps, but it sounds like an ambulance going off.

We have removed the CMOS battery, replaced RAM, reseated all cables but no effect.


Is this a bad mobo or a power supply problem?

Interesting note, we left it running for longer than it takes to being the setup for Windows installation while in the BIOS and it never shutdown, so I don't think it's getting too hot.

 

We just replaced the HD with another one from another one with Windows already on it, and it does the same thing during bootup.

We also tried a Vista CD to run the setup, as soon as we skip the registration key section, boom it fails.

Im thinking the mobo.

 

so no ideas?

 

Any details about the motherboard? Some of the old Compaqs had some really strange setups...

Doesn't sound like a PSU problem, unless something's really loading a rail, leaky cap maybe (some caps make weird noises when failing) - still, I'm with you: I'm leaning towards mobo...

 

I am too...right now, the mobo and whole casing are leaning so far that way it's in the garbage right now. LOL


Thanks all!

 

There is a setting in most BIOS Setup Menus that when enable, causes the PC to boot when power is restored. This is so unattended computers in remote locations will restart after a power failure. So, check your BIOS settings.