iPhone won't stay on-goes off after 10seconds- even without battery

hej there,

i hope u can help me with my iPhone 4s. i worked myself through some guides regarding iPhone repairs. after i installed a new display to an iPhone 4s the batterie connector is off the logic board. bad enough, but the iPhone should power on anyway when its connected to the charger but it wont.

it turns on, shows the apple logo and switches off after about 10 seconds. i checkt every connector, they all seem to fit.

are they any ideas what could be the problem?

thanks everybody!