Computer won't turn on unless you flip PSU switch

[chemeng9]

Hello,

I built my own computer about a year ago and have enjoyed using for gaming and school. Yesterday when I went to turn it on nothing happened when I pressed the power button on my computer. I tried shutting off the power supply and then turned it back on and the power/light/fans started up like when I press the power button but turned back off after only a few seconds. So just to be clear the computer started to boot up when the power supply was turned on not when I hit the power button. I have never had any problems with this computer before and this isn't something I've learned how to troubleshoot yet. I have read a lot of other posts about computers turning off but haven’t found one that has the same problem I do. My computer Specs are as follows:

NZXT Apollo Case
MOBO: ASUS M4A88TD-V EVO/USB3
CPU: AMD Phenom 2 Quad Core 3.2 GHz
RAM: 2x4GB G Skill DDR3-1333 PC3-10666
GCD: Radeon HD 4670 1GB
ASUS DVD Drive
500 GB Western Digital Hard Drive
PSU: Antec EA 650 W

I have tried disconnecting all the power cords and reconnecting them but I get the same result. I tried the reset button (which got stuck) and it did turn on (when the power supply was turned on) and stay on while the button was pressed but shut down very quickly afterwards. If you have any advice or would be willing to guide me through any troubleshooting process I would be very grateful. Thanks!

 

[username-taken]

Ok that's really odd. It started doing that all of a sudden?
Sounds a bit like a mobo issue.
Perhaps clearing the CMOS?

 

[hairystuff]

I had a similar problem ages ago where if I pressed and held the reset button while turning on the system using the power button it would turn on (somtimes needing to pull the power cable and reinserting it), I ended up replacing the PSU and that had fixed it.

 

[hairystuff]

although your PSU does seems like a decent one.

 

[chemeng9]

Ok that's really odd. It started doing that all of a sudden?
Sounds a bit like a mobo issue.
Perhaps clearing the CMOS?

Yes it just happened all of a sudden. I used to put my computer on standby instead of shutting it down but decided I wanted to conserve power so I have been shutting it down instead (for at least a month). I have tried using another power supply and get the same result. I even called ASUS tech support and talked with them over the phone but I had tried everything they suggested so if I want more help I can send it in for them to have their techs look at it. It is under warranty but I have to pay shipping. I am waiting to get some thermal paste I ordered to try resealing the cooling unit to the CPU in case it was overheating but besides that I'm running out of ideas. I don't like the idea of having to ship off my mother board but I'm can't think of what else can be the problem since it is starting to boot before I push the power button. It seems like the power leads are connected already since it starts booting when the power supply is turned on but that doesn't explain why it shuts down after only a few seconds. Anyway I appreciate the feedback and any other ideas you have.