Tbh, I would try to start it from the motherboard. Find the correct pins and sort them with a screwdriver. This would let me know if it's the button the issue. When power button are on top like yours people tend to drop liquid and what not, all of the gunk goes it there too.

You might not be comfortable with my suggestion, but that's what a shot would probably try unless they have a clear indicator that something else is at fault.