The PC (an older dell) wouldn’t start… no lights, nothing.

Sounds like a power supply.

I do the standard thing:

• Get a new power supply from the car.
• Before inserting it into the PC, I rest the PSU on the old PSU, and only connect the motherboard.
• Push the power button and: PC starts up, and then complains (as expected) about no boot device.

So far, its all standard and boring stuff.

I note that the PC has 2 hard drives (both 40gb ide)… one of which is not secured very well, but is unlikely to come loose.

So I install the PSU, plug in everything, close the case (murphy usually strikes if you close the case before trying to start the PC… and then you need to re-open the case).

Yep, I got hit by Murphys law: The PC doesn’t start at all.

A quick look inside shows nothing unusual. I take it back to the office and test the new PSU: it has failed!

I don’t want to risk another PSU just yet, so I to measure electrical resistance of the various molex pins on the HDD and CDROM.

Sure enough, one HDD has the 12 volt “grounded” this is what shorted out both PSUs.

OK, I remove the bad HDD, and “replace” it with the second HDD, get a third PSU, plug in everything, switch on, and I hear a pop and a puff of smoke out of the corner of my eye.

Quickly power off the PC, measure electrical resistance again, and the second HDD now has a short across the 12 volt supply. Luckily the PSU is still OK.

Is this just a coincidence? Or is something “deeper” going on?

I look at the second HDD, and it has a burnt plastic smell, and the circuit board has scorch marks around an IC…

So now I have 2 burnt out HDDs, 2 burnt out PSUs, and the risk of any further repairs causing more equipment to fry.

I decide to cut my losses and tell the customer that the PC is not repairable (and no charge for my shorted power supply).

I also explain that the repair costs can quickly escalate, so buying a new or a used PC is the best way to go.