Leave it plugged in, without battery for a while - see if it boots then. Some rarely used 1x0 machines I've come across take some coaxing to revive, often starting for a moment, power down then become longer lasting. The PB 180c also has a fuse which often dies and an be shunted with thick gage wire.
Another weak point is the PSU, then DC jack, and ensuring the CPU daughter card is reseated and shimmed properly.