I am fairly decent at diagnosing and solving most computer problems but my main machine is totally owning me at the moment. Specs: Asus A8N SLI Deluxe 2GB OCZ Platinum RAM 7800 GTX 500W Seasonic PSU My problems are so weird and varied I'm getting a bit lost: First problem that showed up a few months ago is that computer loads ok, gets to windows logon screen and then turns itself off. After messing around for quite some time I find that removing the network cable(!) allows the computer to boot. So I disable the on board LAN port and enable the secondary on board lan port. Computer works. Same problem crops up, solvable with a remove and swap of the network cable. A new problem, computer won't boot, press the power button and nothing happens. Look inside the case and find that the motherboard power LED is flashing, as far as I can tell this means nothing offical, ie it is not a signal. So I unplug the power and leave the pc for a while, plug back in and it works. Same problem crops up a few times, solvable by removing the power lead for a period of time. At this point I am considering a possible problem with either the psu or the motherboard, but since I do not have a spare psu that is 24 pin and I do not want to waste money I do nothing. Problem seems to get worse, it is now not possible to boot, led continues flashing. I manage to borrow a high powered psu, it is only 20 pin, but I have read that this is enough to power the mobo. I wire it up and it boots, pc blue screens on starting a game, but I sort of expected that since the mptherboard is not been fed its full power requirement. So I bite the bullet and buy a new psu (listed above). Computer still works, however a couple of crashes are later experienced. At this point I have a strong feeling that the motherboard is the culprit. This morning I try to turn the pc on and it boots, gets to windows and restarts, gets stuck at pre POST, no beeps, fans spun up to maximum. I remove a ram stick in desperation, try to boot, I get 1 long beep and 2 short, this indicates a VGA problem, I plug the RAM back in and the pc boots again, try safe mode, pc crashes just as login starts. I remove the other RAM stick, no boot, no beeps, I replace it, no boot, no beeps. This could go on and on, if I remove the power for a while and come back it may or may not boot, it then may or may not crash at windows logon. This is where I am, I am stuck because the symptoms I am seeing confuse me, in summary: Flashing power led, no boot and crashes could indicate psu or mobo, replacing psu has not solved either. Non boot, everything is powering up so this indicates mobo again. Crashes ALWAYs occur just after windows login, in the past removing the network cable allowed full boot. This is tricky, why would a hardware failure on a mobo cause crashes on windows logon? Why would removing a network cable allow a boot, why is it ittermittent? BIOS beeps indicating failed gfx card, the gfx card is fairly new, is the mobo just going crazy and reporting bad errors? If the card really has got a problem, why does it boot sometimes and not others? Maybe a gfx card problem could cause a crash on windows login, but I only got this error code for the first time when I removed a stick of memory, this points more towards a mobo error than gfx. What should my next move be? I have already spent £70-80 on a psu that has not solved my problem, money I don't have, what are the chances that replacing the mobo will still leave me with a bad system?