I was rebuilding a machine that got fried, old board/processor were no good. I got a new MB, power supply, processor, RAM, vid card. I installed everything, but the machine will not turn on if the old hard drive (WD sata drive) is connected to the power supply, let alone the sata cable to the board. If I unplug the power to the drive and turn the pc on, it posts. If I connect power to the drive, pressing the power button on the case does nothing.
Is there anything I can do besides toss this drive in the trash? I've never come across this situation before. I at least expected it to boot and give me some errors.
I had an odd problem like this a couple of months ago. The computer would power on with the hard drive connected but it would just display the motherboard's splash screen and wouldn't POST. I thought about simply chucking the drive away as I figured it must be broken but first I tried it in another PC to see if it worked. It worked fine so I formatted it and put it back in my PC where it has worked fine ever since. If you've got another PC that you have access to I would recommend at least trying this.
Yes, try what dangerman200k suggests - test old HDD in another machine.
However, have you considered that the event that "fried" all your other components actually damaged the HDD, too? It may be dragging down a critical PSU output because of its own damaged circuits. If that is the case, the test in the other machine will probably do the same.