Built computer won't start with motherboard installed in case.

Hello,
I just finished building my second computer yesterday and after checking to make sure everything looked right I pressed the power switch to start it. The system started to turn on but immediately blinked off after about a quarter-second. After unplugging everything I checked to see if all the components were secure and nothing extraneous was contacting the mobo, then I attempted to start it again with the exact same results. After searching this site for possible solutions, I found a list of things to check and went through them one by one. With no solution found, I disassembled the components, pulled the mobo out and reassembled it outside the case. When I completed the power up circuit the system started perfectly. I confirmed that the case standoffs are in the right positions and only have as many as are mounting holes in the mobo. I reinstalled everything and attempted to start with the exact same results as before, no powerup. Anyone have any ideas on what I may have missed?

A good start on problem determination.


My suspicion at this point is that there is a short in the case front panel wiring, or the front panel connectors are miswired or mislabeled.

Disconnect those wires, and try to start the motherboard in the case with the motherboard pwr button if you have one, or with a screwdriver if not.
Then, attach the front panel connectors one, by one, and retry.

Double check that the front panel wires are connected to the proper pins.
If, for example you connected a hdd or pwr led cable to the reset pins, you would get similar symptoms.

I'm wondering if maybe one or more of the mounting screws are somehow short-circuiting the board.

I actually did notice that there appears to be sloppy soldering around the mounting holes. I will check that first and if that still doesn't work then I will try installing one part at a time and testing.

Ok, I tried all the possible solutions in this thread so far, none have worked. I even lined up the mobo with no mounting screws and no i/o plate and nothing installed and it still wouldn't start up. Still starts fine out of the case. I am officially out of ideas.

Ok, here is the setup:

- AMD FX-6100 Zambezi 3.3GHz Socket AM3+ 95W Six-Core Desktop Processor FD6100WMGUSBX

- GIGABYTE GA-990XA-UD3 AM3+ AMD 990X SATA 6Gb/s USB 3.0 ATX AMD Motherboard

- CORSAIR Vengeance 16GB (4 x 4GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model CMZ16GX3M4A1600C9

- XFX HD-687A-ZHFC Radeon HD 6870 1GB 256-bit GDDR5 PCI Express 2.1 x16 HDCP Ready CrossFireX Support Video Card

- XCLIO Windtunnel Fully Black Finish 1.0 mm SECC Chassis ATX Full Tower Computer Case

- Corsair- Gaming Series 700-Watt ATX CPU Power Supply

Plus of course various SATA HDD/optical drives. I will take some pictures tonight when I get home from work. I'm also going to remove the mobo and install the standoffs and mounting screws outside the case to see if it will start.

i also had the exact same problem i fixed it by replacing the psu (obviously not the problem in your case)