How to fix dead board

How experienced are you with electronics? If you're looking to repair a circuit board that won't power up, you'll need a set of schematics and board view (gerber) files, along with a good multimeter with fine tip probes. You'd need to start with the power circuits and verify the power management chip is working, and possibly trace through the circuitry to locate any shorts or open circuits. Some people use a thermal camera to locate hot spots indicating shorts, but there are other methods available as well.

Is that the sort of thing you had in mind, or are you thinking more along the lines of replacing a board? What kind of troubleshooting have you done so far that makes you think the board is dead?

Honestly, you haven't given us much to go on, not even which phone you have. If you want information on actually fixing your phone, we'll need to know what model you have. The more you can tell us about what's going on with your phone, the better chance we have of being able to help.