Computer case power button problem?

[brownbox]

The problem is when I turn off my computer, whether it be through windows, or by pressing the power button which I have set to shut down, my pc turns off. As normal you hear the drives and fans power down and then- Vrroom Woooooshhhh, the computer turns itself back on within 10 seconds! Dont know why its doing this, but I swear, I didnt touch anything!
So whenever I try turning my computer off, it turns off then starts up again!The only way I can turn it off is to switch it off at the wall, power supply, or unplug it. But the thing is, if I hold down the power button (like when the computer freezes and you turn it off), the computer turns off and stays off.

Could this be the button? If not, how can I fix it?