No boot/video

Hello,

When i power my computer all the lights and fans kick on but i get nothing on the monitor and i get no beeps nor do i hear the window start up chime. I am using my onboard video card, i know it is not the monitor because i tried it on another PC and it worked and i still would have heard sound. Most forums that i read said it could be the video card. I took a video card(AGP) from another PC and tried it in mine and got the same results no start up no bios noting just fans and lights. Does anyone know what is wrong, could the power supply be bad even though my fans and light still work or maybe the motherboard? Any advice would be great so that i don't go out and waste money on parts that i don't even need.