Q: What problem are you experiencing? A: My computer will not turn on Q: When you hit the power button, what happens? A: The computer seems to turn on, but nothing appears on my monitor. Q: When you turned the computer on, did you hear a beep? A: No, there was no beep. Q: Does the keyboard numlock light function? A: No Q: Does disconnecting all peripherals make any difference? A: No. Q: Are you comfortable removing and reseating the memory and video card? A: Yes. Q: Does reseating the memory solve the problem? A: No. Q: Does reseating the video card solve the problem? A: No. I had once earlier (a few years ago) similar problem. Back then I discovered that it was because of RAM so I had to buy another one and it fixed the issue. But now I have the same problem again and I bought replacement for RAM but this time it didnt seem to fix the issue. I have quite a many times turned on the computer with nothing more than just RAM (Ive changed the place where I seat the RAM) and video card connected to computer, and mostly it doesnt display anything but sometimes it turns on and I get to BIOS loading screen (not the usual one, but the one with errors about not having keyboard connected, etc.) and after that I get the error about hard drive not being connected, so I turn the computer off and connect the hard drive on and the computer wont turn on anymore. One time I tried accessing BIOS settings with just RAM, video card and keyboard connected but after accessing BIOS all just gets "stuck" and my keyboard seems to stop working. Now it seems that it wont turn on even with just RAM and video card connected... I tried testing out my PSU (500W) if it was dead but the fan comes on so I think the problem isnt with PSU. Perhaps the problem is with motherboard (ASUS M4A77TD PRO)... I've even tried resetting the BIOS by using pin and taking off the battery but it didnt fix the problem either....
look at the silver top capacitors on the notherboard to see if any are domed or leaking brown stuff. try another psu just because a fan is working does not mean the other voltages are as fans use 12v but motherboard also needs 3.3v & 5v.
It sounds to me you have not correctly hooked up all the wiring in your pc. Things you need to do Read your motherboard instruction Guide Not all new computers make a beep when they start that is a thing of the past You will have some small pins at the bottom of your motherboard where your HD Led power switch and so on are connected. Make sure these are connected correctly to the correct pins and + is in + and - is in - I reckon this will solve your problem.