My favorite client calls are the ones with unusual problems. Today I visited a Mac Pro that was having startup problems. The owner was quite good at his own maintenance and repairs and had done all the tests I usually do. The symptom was a refusal to get past the blue screen to the desktop. It reacted to a reinstall of Leopard, but with updates it went back to failing. Finally it wouldn't start from the DVD.
Aha, I thought, typical example of problems with the 10.5.8 update. Nope, I could not get it to start from my FireWire drive running 10.5.6, or another volume running 10.6.2. It wasn't a graphics failure because it would correctly display the startup alternatives from holding down the Option key.
Thinking it might be loose RAM or something, I went to reseat the modules, but he told me he had already tried that.
So I pulled his drive out completely. I wanted to boot ONLY from my external drive with no chance of interference from plugged in devices. That didn't work either.
I noticed something strange when I peered into the case, which was under a table and not immediately obvious. I looked at the back and yep, every slot was filled with a display card! He was running a standard 30-inch display, but he had the capability of running EIGHT displays.
"Did you order this with all those video cards?"
"No, this was a standard order from the online Apple store, in September of 2007."
It had been working fine up until the Software Update, all these months, with all those cards in place. A video card is supposed to be inactive until a display is plugged in, but something must have happened to one of them as a result of the update. So I removed all three of them, leaving the standard one he had been using all along.
It booted perfectly from my FireWire drive. I shut down and plugged his internal drive back in, removing mine. It booted perfectly. No repairs needed.
He still has no idea why he got a Mac with all those extra cards, but they will wind up on Ebay once he tests each one to see if one is dead and causes the problem to return. Outside of some headaches, he will come out ahead selling the cards and deducting my fee for the visit. Took me just under an hour.