If the issue is the power button not working and you can get it to turn on use the f2 key to get to the bios screen. In there find the option to turn on with A/C. Or turn on after power failure. and select it.
Then if you run into the power button no turning on, just unplug the A/C and plug it back. It will turn on when the A/C is plugged back in.
I have the same issue with a precision m4800 (very expensive laptop). I tried everything, replaced the power button pcb, replaced the bios battery, flashed to the latest bios, plugged it in to a docking station (even the docking station power button will not turn it on). But with that A/C set to turn on, I can get it running by unplugging A/C power and plugging it back in.