ust had the experience and would want to share you..
this Computer was brought to me by the owner asking help, his computer keeps turning off after a few seconds,
I tried using a working Power supply and still its occuring
tried the old power supply to my board and it works fine
tried checking the on and off swith on the casing.. and hmmm
there i found the problem
The on off swith was not properly aligned to the casing's on/off button
did a few fixes and it works as new again..
the On-off swith was not being pressed properly causing the flow of electricity inside the board go temporarily..
hope this helps..