Mac Pro 2009/10 Doesn't boot after weekend, LED shows for 2 secs then nothing! One of our users computers on the network has a ~2009 Intel Mac Pro. On Friday the machine was fine, shut down correctly at the end of the day as normal.

This morning (Monday) the Mac Pro will not power up. After pressing the power button we get 1-2 seconds where the "on" LED is lit, then it goes off. We have removed all components, and blown with canned air, reseated everything, reset the SMC, but still the same issue.

The Mac Pro has 2 DIMM "boards", one of which is full (4 slots) and the other which has 2 slots free. On the brief power-up, all 4 LED's are lit on both DIMM boards, they're not on long enough to do anything else, is this normal? We've reseated all the RAM and the boards, but no change. We've even removed components such as the graphics card, and sticks of RAM individually but no change.

I've read that if the system detects no RAM it will beep 3 times, we removed all the RAM but no beep, I think because the system is not powered up long enough.

Any suggestions? We think it's a PSU but can't be sure.
We just managed to figure this out. It was a faulty RAM board/riser. We found the DIAG switch and pressed it with a pencil, all the lights for the PSU checked out properly. So we went back to thinking it must be the RAM again. One riser had 10GB on the other had 2GB, luckily the 2GB one appears faulty. We removed this riser (although we'd already done this!) and the machine booted up fine!

We then reseated the sticks in different slots on the faulty riser, reseated the riser and the machine booted, but couldn't find the RAM. So for now we've ditched that riser and are letting the machine run with 10GB instead of 12GB.

Hope this helps.