motorola z3 problem

hi everyone,

i have a z3 here which wont start.

when i charge the battery the display is working, telling me something like battery charging and when its done with it the battery display shows 3 dark columns. when i disconnect it from the charging cable there comes some sound and then nothing anymore, just stays turned off. when connecting it back the battery display has one dark column and two yellow blinking ones for some minutes, then it changes back to 3 dark static columns and tells me charging finished.

also the outer and inner keypads lights are working.
when pushing the startup button nothing happens.

my two guesses so far are: either something is wrong with the battery or the startup key is just not working.

before i start disasembling or anything i need to figure out the battery:
1. i dont know about the meaning of the battery display. is the behavior i described normal?
2. as long the phone is connected with the charging cable, shouldnt it work even with a bad battery?

maybe anyone here knows more or has any good advice for me. i appreciate any help you can give me

cheers