Hi there, I have been reading forums for days now and trying all the various suggestions I have found, but still have no joy in fixing this unusual problem. If anyone could offer any advice at all I would be incredibly grateful! I run the following setup: Asus P5K3 Deluxe Motherboard 650W Dark Power Pro "Be Quiet" PSU Intel Q6600 Processor Gainward 9600GT Graphics Card (1Gig) 2GB Corsair TwinX DDR3 RAM 750Gig Samsung HD Phillips DVD-RW (not sure of model number, now disconnected from PSU and mobo) HP 2408 24" Monitor using HDMI cable I switched on the PC one night last week and got a black screen. No POST, no BIOS, nothing. Admittedly a week before I had tried to switch it on and it didn’t boot, but I just turned it off and back on and it went fine. The green motherboard LED comes on solid so there is power, all fans spin up including the CPU fan, the hard disk spins up, and then it just seems to "stall", and does not even POST never mind go into BIOS or start to boot. I know that it definitely is not just booting up and not outputting to the screen, as the graphics card fan stays at full speed, normally during boot once the driver is loaded it slows down to dynamically maintain temperature whilst reducing noise. If it was simply not outputting to the screen then this fan would slow during boot, even though I can't see the output. It was built in May and has worked absolutely fine until last week. I have not added any new hardware, loaded drivers, flashed BIOS etc. since May. I have gone through the following steps to try and resolve it: 1) Borrowed a known working monitor, then graphics card, fault remained 2) Bought new identical RAM, fault remained (I was going to upgrade to 4 Gig anyway!). Also tried all combinations of single/paired modules 3) Bought new identical motherboard, intending to return the old one if that was the fault, put my CPU, PSU, graphics card and RAM in the new motherboard on a test bench and the fault remained 4) Put my CPU in another known working socket 775 PC – it ran absolutely fine 5) Also put my graphics card in the same known working PC, again it worked fine 6) Replaced CMOS battery – no help All of the above leads me to believe the PSU is faulty, as the fault did not occur when I used my CPU and graphics in the known working machine. My next test is to borrow a PSU so I can rule out a fault on the EATX+12V rail that supplies the 8pin connector on the P5K3 board. However one thing confuses me a great deal; I can get the PC to boot, probably half the time, by clearing the CMOS i.e. switch off at mains, remove CMOS battery, and bridge the appropriate jumper. This works about half the time as I say, though this may be due to me not giving it enough time to clear properly (I am getting frustrated now and hence impatient!). For example, last night I got home from work, set the CMOS to clear, made dinner, then put the jumper back to normal and it booted fine, then I just pressed F2 to load setup defaults and I enjoyed 5 hours of trouble free computing. Sure enough when I turned it off when I was going to bed, I tried to reboot and it would not POST. I fail to see how a PSU problem would cause this behaviour, which makes me think it is either a motherboard fault, or a fault with the BIOS chip or CMOS battery. But surely the odds of me getting identical failures on 2 consecutive boards is basically impossible? And I replaced the battery and have checked voltage on the original and replacement and they are both showing 3V. The easy solution would of course be to leave it running constantly, but it is right next to my bed and the noise from the CPU fan with dynamic fan speed control (which is the BIOS default) is unbearable! If anyone has any ideas I would love to hear them, otherwise I will post the results of my PSU trials if/when I can borrow one!