hey, i got a new mother board with ATX and it have 24 pins and my old power supply has 20 the manual i got from MSI says i can use it..... but i hooked it up and i cant.... can anyone help me?

Thats because it needs the additional power connecters in the 24 pin connector. you could try a 20 to 24 pin adapter but the best solution would be a new psu.

What do you mean when you can't use it? it doeesn't turn on?

He's sticking a 20-pin PSU connector into a 24-pin mobo connector. He's missing 4-pins. Now, I've heard that some mobos will work with 20-pin connectors, but stability isn't guarenteed. I make the same suggestion as ccokeman, get yourself a nice 20-pin to 24-pin converter and things should be peachy.

I know that, my question was whether it turned on or not. He alread stated that he was sticking a 20 pin male into a 24 Pin female.

NinjaDude:

What are your system specs? (PSU, mobo, etc.) This will help us to diagnose your problem.

Did you insert the connector in correctly? The individual pins are keyed to prevent incorrect installation.

Other than that my guess so far without further info from you is that your motherboard is grounding out on the case, or one of your components is dead (mobo, CPU, ram, etc.)

Reguarding 20 to 24 pin "adapter" cables:

They are COMPLETELY worthless. Read the PSU FAQ (post #7) for more info.