Turns on for 5 seconds

[omck]

Hey guys! I've ran through a lot of topics but couldn't find the answer.

My cousin, a while ago unlocked MY iPhone 3gs and changed battery on it. Now it doesnt turn on at all, only when I plug it in the computer, it turns on after 5 min for 3-4 seconds so I see an apple logo, and the it turns off and it repeats every 1 minute when it's plugged in.

 

[coast]

Seems to be a hardware issue. Have you tried checking the connection to the battery?

 

[omck]

I think that the connection to the battery is ok because the phone turns on(logically) but anyways how do i check connection to the battery?