System starts up but then shuts down

[pigeoncracker]

My computer has been running fine for more than 3 years and then I decided to clean out all of the dust and replace the thermal compound. Now when I started it up 6 light on the motherboard came on and all the fans went on too. Then after about a second it turns off then restarts. I have reset the BIOS and taken the motherboard out of its case with just the cpu and motherboards power supplies hooked up and on a cardboard box. still does the same thing

specs
motherboard gigabyte ep45-ds3r
ram NVIDIA ocz2n800sr4gk
cpu intel core 2 duo 3.0ghz
gpu BFG tech GeForce GTS 250
power supply RAIDMAX RX-530SS

 

[SirGetch]

Is your HDD or SSD first on the boot priority?

 

[Chicano]

Not trying to be funny here but... it's acting like it's overheating. So check all CPU cooler parts are set right:
1. Is the CPU fan power connected to motherboard?...
2. Is the heatsink firmly attached to the CPU (The pressure cam, lever, etc. may still not be engaged).
3. Did you use the right amount of thermal grease? too much can be just as bad as not enough.

Can't understand is what you mean by two power supplies hooked up. (????)

 

[Chicano]

Did you double check the front panel connections to the motherboard header?..
The power button pins on the motherboard for example; if they are bridged and stay bridged, the computer will start and reboot like that.. so check that this connections are correct. If you have any doubts on this, check the motherboard PDF manual available from the motherboard manufacturer's mobo model downloads.

 

[pigeoncracker]

Not trying to be funny here but... it's acting like it's overheating. So check all CPU cooler parts are set right:
1. Is the CPU fan power connected to motherboard?...
2. Is the heatsink firmly attached to the CPU (The pressure cam, lever, etc. may still not be engaged).
3. Did you use the right amount of thermal grease? too much can be just as bad as not enough.

Can't understand is what you mean by two power supplies hooked up. (????)

no the cpu power cable and the main one
the cpu fan is connected and all the fans turn on when it starts up. It is firmly lacked onto the motherboard but I am getting a new one soon to try it. I used a grain size of thermal paste in the middle of the cpu. There is nothing wrong with the power button pins

 

[pigeoncracker]

• 
  

Is your HDD or SSD first on the boot priority?

my hard drive should be on first boot priority

 

[pigeoncracker]

Could It be a problem with the Power supply?

 

[Chicano]

It's possible!... what the Power switch actually does, is turn the PSU on, and if you jump the power switch pins on the motherboard and hold the jumper on, the PSU is what loops on and off... it's like when from Windows, you press and hold the start button... the system shutsdown within 10 seconds... the difference is Windows controlls the shutdown to save data. So, it may be possible but I won't assure it.. you'll have to try a different PSU to test..

Same problem here turned out to be a lose wire connection... check it.
http://www.tomshardware.com/forum/378412-31-turns-turning

Also same problem here... someone's comment indicates a failing PSU
http://www.overclock.net/t/952436/computer-turns-on-then-off-after-a-second-psu/10

Same here... turned out to be the PSU
http://www.overclock.net/t/952436/computer-turns-on-then-off-after-a-second-psu/10

 

[pigeoncracker]

It's possible!... what the Power switch actually does, is turn the PSU on, and if you jump the power switch pins on the motherboard and hold the jumper on, the PSU is what loops on and off... it's like when from Windows, you press and hold the start button... the system shutsdown within 10 seconds... the difference is Windows controlls the shutdown to save data. So, it may be possible but I won't assure it.. you'll have to try a different PSU to test..

Same problem here turned out to be a lose wire connection... check it.
http://www.tomshardware.com/forum/378412-31-turns-turning

Also same problem here... someone's comment indicates a failing PSU
http://www.overclock.net/t/952436/computer-turns-on-then-off-after-a-second-psu/10

Same here... turned out to be the PSU
http://www.overclock.net/t/952436/computer-turns-on-then-off-after-a-second-psu/10

Tried a different motherboard and did the same thing. Then tries a different power supply and the same motherboard and it worked! Doesn't have enough voltage to support my graphics card though