My computer is shutting down after start up , please help me ,?

my computer is shutting down just after start up , mother board Asus P5N Mx , hard drive Hitachi , processor : intel Core 2 duo , Dvd writer : LG . i had frontech desktop speakers when i attached then to the computer the problem started at that time , i taken them out now . It's not starting at all . i took out the panel on the tower of the computer the motherboard has a green indicator light , have a microtek Ups . please some help me