Power Supply or Mobo? Something else?

[John Williams]

Last night my system was working fine. Today I woke up this morning and my PC wouldn't finish booting. It would get to the logo screen ("Press DEL to enter setup, Press TAB to display POST") and stay there (it won't won't respond to the keyboard, so I can't see the POST or access the BIOS.)

I opened her up and:
~Removed RAM
~Swapped RAM to different slots, both sticks and single
~Reset the CMOS
~Removed all external devices
~Disconnected all IDE/SATA/Etc devices
~Removed all cards
~Checked for any visible damage to components

Nothing works. The outlet/surge protector are fine. I sometimes get a POST beep, I sometimes don't. I sometimes get to the logo screen, sometimes the monitor never gets kicked on. Some of the time it won't power on at all. A few times I've hit the power button, had nothing happen, then five or ten seconds later it powers up.

I have:

Mobo: ASUS P5N-E SLI LGA 775 NVIDIA nForce 650i SLI
Processor: Intel Pentium D 925 Presler 3.0GHz LGA 775 95W Dual-Core Processor
RAM: CORSAIR XMS2 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400)
Video Card: MSI NX8800GT 512M OC GeForce 8800 GT 512MB PCI-E
Sound card: Soundblaster Audigy 2
Power Supply: Thermaltake Silent Purepower W0014RU 480W ATX12V

Everything except the PS and the sound card is fairly new - Christmas for the mobo/proc/RAM, two months for the video card. My best guess right now is the power supply, but I can't be entirely sure. I'm on disability, so I don't have the option of troubleshooting by throwing money at it (IE - I need to replace the broken component, not everything that could be broken.)

 

[robisbell]

get a electrical outlet tester, and a heavy duty voltmeter to test it and the psu.

 

[John Williams]

I found another power supply and tried switching it out and got exactly the same result. Is there an easy way to find out which component needs replaced? I don't have another mobo with the same socket.

 

[HdwGuy]

I know you said all external devices were disconnected but i had a problem like this that was caused by an USB scanner. Unpluged and worked the thing that tipped me off was it would get to the list of devices and hang. Could not get into bios etc. USB being the last device shown in the list. Unpluged scanner and everything worked. Have you tried another keyboard?