MP 1,1-5,1 Dead Mac Pro 2009 4.1 (flashed to 5.1)

[HenryMacPro]

So, last Sunday I tried to start my Mac Pro, but nothing happened.(Not sure if it switched itself off, as I sometimes keep it on.)
When I unplug the power cord and put it back in all I see is 1 red LED turning on for a moment and that’s all....(located just under the first HDD bay)
Pulled out almost everything, all pci cards, all drive bays are empty, change onboard batter, but still no luck.
Any suggestions what check next??
My first guess faulty Power Supply??

 

[Snow Tiger]

Do you have access to a watt meter ( like a Kill A Watt consumer device ) ? Testing for the trickle charge is a good indicator of a working PSU . But you need to unplug your Mac for around 12 to 24 hours before checking this , to allow time for the caps to discharge naturally . The test takes just a second as you plug in your power cord back into the Mac for the first time after this rest , so you have to be quick to read the device readout before it goes back to zero watts . Expected result for healthy Nehalem cMP is around 20 - 25 W trickle indicator .

 

[HenryMacPro]

I tried it, looks like it fluctuates between 20, 30 and down to 10 Watts (or my meter might be wrong..)
it’s actually 2 red leds that flash, CPU A & B. Pushing the diagnostic button makes the amber (5 V?) light up...