Old Computer, New Problems

I took apart everything off my Compaq Presario which use to run Windows 98 SE. I tryed to put it back so i can have another pc but when I connect the hard drive,Video card,Power supply and the power button, It turn on but there is nothing on the screen. I have a Sony CPD-G220R monitor which works great on my other Compaq. I’m using 3Dfx Voodoo 3 video card. Could any one help me solve this problem. (Q: How can I get my monitor to show up on the monitor?)

Thanks,
Nikita Kotov