Trying to see if an old Dell PC is still operational, but can't turn power it up

[Udgnim]

PC is an old Dell 2400

have an older (working) HP hard drive and a PC power button (used Dell case for different PC setup) as non-Dell items hooked up to the motherboard. so the motherboard and everything attached is out in the open right now.

when the PSU is plugged into the electrical outlet, the exhaust fan and PSU fan spin up, the motherboard light is on, and the light code before POST is the following:

Problem Description: "The computer is in a normal off condition; the computer is connected to its electrical outlet."

Suggested Resolution: "Press the power button to turn the computer on.

If the computer does not turn on, ensure that the front-panel power light is on. If the power light is off, ensure that the computer is connected to a working electrical outlet and then press the power button."

I've plugged in the PC power button into pins 6 & 8 of J28 (link below has motherboard layout) assuming pin 1 is the lower left, but the PC doesn't power up other than the fans and mobo lights already being active.

http://support.dell.com/support/edocs/systems/dim2400/en/sm_en/techov.htm#1105465

anyone have an idea of what I'm missing or not doing? thanks

 

[Fardringle]

Do the fans spin as soon as the computer is plugged in to the electrical outlet, or only after you push the power button?

 

[Udgnim]

Do the fans spin as soon as the computer is plugged in to the electrical outlet, or only after you push the power button?

they spin as soon as the computer is plugged into the electrical outlet