Mac Pro 3,1 graphics card puzzler

[rodmonkey]

After running a Radeon 5770 for 3 years, it suddenly quit - the computer crashed and wouldn't reboot. I replaced it with a 5780, which ran nicely for three weeks, then boom! one day the computer wouldn't boot. After 2 more 5780 replacements that all worked for two weeks, and the last one not at all, I threw in the towel and bought another 5770 - can't go wrong with what worked, right? The computer worked for a week, then I came in to fine it turned off and unable to boot - the power LED wouldn't even come on. Took it to the Apple Store, and they tried replacing the riser board, the power supply, and the main logic board, and eventually they decided it was: the video board. Which they can't replace or apparently even talk about, because it's not certified for my machine.

I suppose I could get a "certified" board and drop back to FCP 7, but clearly something's changed in my Mac Pro that it won't run the higher end boards and I don't even know where to start! Any ideas?

It's running 10.8.5, by the way, on 10G of memory.

 

[gpzjock]

Have you tried running it through a UPS?

 

[rodmonkey]

Always do.

I found someone else in the area who has the same model Mac Pro, so I'll see if the "bad" 5770 board works in his machine, and if his board works in mine. Side note: I gave him my old 5780 that wouldn't work, and it seems to work for him. Danged if I know what's going on!!!

Have you tried running it through a UPS?

Additional info: popped in a Radeon 5770 that had been running for a year in an identical Mac Pro. It ran fine (with a glitchy start) for several hours, and then crashed. Now I'm back to a non-booting machine. WTF?

Oh well. I hadn't planned on buying the 1st gen nMP, but plans change.