powers down when unplugged battery not works

dear people,

i have a issue, when i plug in the power addapter in my iphone the apple logo starts to blink.

when i take out the power addapter is turns off.

replacing battery and/or dock connector didnt work.

when i put the usb cable in my computer i can get it to give the "connect to iTunes logo" on the Phone.

the iTunes sees the Phone when i try to restore

but then it gives me a iTunes error 21.

the Phone had waterdamage before

what can i do to check if the Phone wil work again?

thanks and hope to get help.