I have a computer that I recently had to replace the power supply on because it basically gave up and died. I started with just the motherboard connected to the power supply, and that worked. obviously I couldn't boot since I didn't have a hard drive powered on. I then connected my one "master" hard drive and could boot to windows fine. I plug in my "slave" hard drive, and the machine won't even power on. the motherboards lights turn on when I turn the switch on the back. but if I press the power button, I can see the fan on the cpu spin for a split second before it stops. almost like there is a short in the power or something. I disconnect that hard drive, and everything turns on fine. Is the logicboard on the hard drive bad? or could it be something else? I have tried multiple other power plugs from the power supply, so its not just a bad one from it. Thanks for any information.

When power supplies fail, they can damage anything connected to the mboard, including the logic board on a hard drive, especially if something shorts in the PS while it's dying. The PS may produce too much voltage while failing and that can fry anything - usually it tends to fry floppy and CD or DVD drives first. If the PS is an el-cheapo, it's more likely to damage something - better PSs have several features that are a lot more likely to shut down the PS before it can damage something, including anti-short and over voltage protection. You didn't mention removing to the power to the computer case / the power supply when you were plugging in and unplugging the slave drive. You must always remove the AC power to the case whenever you unplug or plug in anything connected to the mboard - ATX PSs are always powering ATX mboards in some places as long as the AC power is connected to them, even when Windows is Shut Down or in Standby or Hibernate modes. E.g. A small arc while plugging in or unplugging the hard drive can instantly ruin the logic board on a hard drive, or fry your power supply.

I did unplug the ps from the wall every time before doing anything internal to the computer. I know that can always cause a problem. I also noticed that the one hard drive that does work gets a S.M.A.R.T. error on boot. I downloaded a hard drive monitoring software from panterasoft.com that reads the smart system stuff. and it says that the hard drive temp is high 47C. I can definately tell that the hard drive that works is rather hot. So It looks like when the power supply went it might have killed one hard drive, and serverely hurt another.

47 is on the high end of normal. If the hard drives that works is a slim model - a lot less than the usual close to 1" thick - they have a reputation of running hotter. In any case, check that hard drive. See the latter part of response 1 in this: http://www.computing.net/windows95/... If the drive passes the diagnostics, you could try one of the hard drive coolers with it.

If you have BOTH HDs on the cable jumpered to master, that can cause the system to hang.

"If you have BOTH HDs on the cable jumpered to master, that can cause the system to hang." True, but that would not cause the symptoms he's described.

Yes it would.