MP early 2008 won't boot - nVidia 8800 fan spins at maximum

Hello everyone

My trusty Mac Pro 3,1 won't boot suddenly.

When I press the power button the nVidia card's fan spins at maximum and doesn't stop. That fan normally spins up for a few seconds quite loudly and then settles down but now it doesn't stop. The pale blue light at the power button blinks continuously and the only thing I can do is to press and hold it in until the computer shuts down.

The only thing that has changed recently is that I installed a Sonnet Tempo Pro with two SSDs. However, that went without trouble. I installed Mavericks on them as a striped array when attached to the backplane, tried booting a few times, installed a bit of software and all was dandy. Then I set the boot volume back to the original Lion installation on another drive. I go away for the weekend and discover this inability to boot when I come back.

I suspect the video card fan's behaviour indicates that it might have broken?

I've tried replacing the CR2032 battery and done a PRAM reset without improvement. All lights on the RAM risers glow red and the RAM sticks are properly attached.

Thanks for any insights.

Oh another thing - if the card is fried, which more modern cards can I install?

Cheers
Philip

Thanks for the reply Jake.

My normal Lion boot volume is currently selected as boot volume. After I installed Mavericks on the Tempo SSDs I changed the boot volume back to the Lion volume.

So I don't think this is related to the Lion volume. After work today I'll see if I have another drive lying about which I would pop in and try to boot from.

I tried the graphics card in slot 2 but no change. Unfortunately, I don't know anyone with another graphics card I could try etc.

I also tried booting from the original installation DVD (I had to dismantle the computer and open the DVD drive with a paper clip) but it doesn't boot from the DVD.

I really hope it isn't the logic board. If it is, can I buy one of those myself and install? I'm pretty handy but perhaps that's a very complicated operation.

About a new graphics card - I thought only a few cards were made for the Mac Pros and OS X. Perhaps I'm misremembering.

cheers
Philip

Yeah it's strange. Thanks for the info about the drivers. I didn't know this.

The cheapest first step is, I think, to just get a used gfx card and try out. Then take it from there. Fingers xed.

Thanks a lot for taking the time to help.
Philip

Thanks everyone. I removed the nvidia card but no joy. So off to the apple centre. We'll know in a week what it is.

Thanks again.
Philip

I forgot to update this thread. The problem was faulty RAM. Yes I felt like a major fool for not having noticed this. However, the red lights on the riser didn't come on though so I didn't look for this. Luckily the tech didn't think of it either and actually fried a new riser that he had put in, thinking the riser was broken. So while I could have bought a riser myself I would likely have placed the faulty RAM back on the riser and fried it. This meant the repair cost was actually cheaper than buying two risers.

In any event, all's well now.