My computer power button wire get break what to do. Any idea

If you are unable to repair it on your own by soldering it, you'll have to buy a new cable or power button that includes the cable.

Here is a couple of things to try:-

1 - Take the front panel off your pc case and try pressing the button which would normally be behind the power button.

2 - Look for a cable running from the power button to your motherboard. Take this cable out of the motherboard, give it a blow and put it back in and make sure its in.

3 - Replace the wire that goes from the case to the motherboard

4 - If you get no power, no fans, no beeping, nothing. Replace the PSU.

These are the steps i use. But you can use these steps for more information:

What kind of computer do you have? Does it have a brand name or model number?