Hi, I have an issue: several years ago I received a Mac Pro 4.1. Quad-Core 2,6Ghz, 3x1GB RAM, 640GB HDD and a GT120 gpu. I've flashed the Mac Pro towards a 5.1 model and installed an Intel W3680, 3x8GB DDR3 ECC RAM, a EFI flashed Radeon HD7950 and a Samsung SM951 512GB m.2 SSD on a HyperX PCI-E adapter. I've used this setup for more then a year until last week the unit started to freeze. Some random freezes, I've experienced it for 3 times last week. Coolers kept spinning, no hard drive activity and the screen stayed blank. After a hard reset, the Mac Pro worked again until a couple of days ago, now the unit can't boot anymore. I can't even hear a chime, nor see disk activity... I think the unit is dead. I've googled (and found the service manual) and tried several "cures" in the hope to revive my MP. Tried the minimal startup without memory, placed the original cpu, gpu, memory... back in. Nothing seems to help. I even replaced the BR3032 battery and checked the northbridge heatsink (that one is still attached fine). When I plug in the power cable, the 2 red led's on the motherboard and the one on the cpu-tray are visible turning on and off (normal behavior). When the unit is off but the power cable is attached, the diagnostic led for 5V is solid amber. When powering on the unit and checking the leds: PSU (solid green), 5V (solid amber), SYS PG (solid green), EFI DONE (solid green) but GPU OK keeps blinking green. The front led is solid white. It's not blinking. (even without memory, the front led stays solid white) I don't understand why the system is not booting, is not giving a chime and the diagnostic led is blinking on GPU OK even there's no gpu connected in the system. fyi, cpu (the w3680) and northbridge temperature was always around 40 degrees celsius, memory (3x8GB) around 40/45 and the disks around 35. Any thoughts?