PC not booting

Hello majorgeeks.

i have this problem, my computer dont boot at all, when i push the switch, the fans starts up, and it sounds like the CPU does aswell, cant hear anything coz of the fans :b but then it shuts down?? and when i completely power off the computer (at the PSU), and turn it on again, the computer can only be started once, then i have to deswitch and switch it on again, before giving it another try.
nothing appears on the screen, there is no time for that, it seems like the power only goes on for 5 secs.
Any sugestions?

 

all connections have been checked, all the important.
have nothing changed, i played on it yesterday, and today it dont starts, only for 5 secs, and then i shuts down again, i did try to remove the motherboard battery for ten min, and did try the ram thing, (one at the time) no response, same problem though. no beeps, so hardware are working proberply, and i do get the CPU init on the LCD poster.