my pc will turn on but then goes off

[estorer]

Hi - I'm having trouble with my PC. When I press the power button, it will turn on; however, nothing displays on screeen and the computer restarts itself without displaying bios (or anything else). I've tried pressing buttons on the keyboard in the hope of getting into bios; however, this does not work. I am not sure what the problem is or how to fix it. Thanks in advance for any help.
p.s. it says im online but its just my laptop being kept on

 

[customisbetter]

bad power supply. I have two that do that.

 

[dragonsprayer]

remove on ram stick and alternate slots and ram sticks - does it boot?>
you need a bios change or the ram is going
disconnet everthing you can one item at time does it boot?
but first check the hsf make sure its not loose or ram or anything else

swap the video card if you have another one after you try above

 

[cats_Paw]

its probably a bad power supply, if your motherboard is good, it shuts down computer to prevent damage (happened to me and im thenkfull for it),

plz post your computer specs fast so we can help u not fry your components.