iPhone 5 won't respond after water damage, teardown & screen replace

Perfume bottle burst in girlfriends handbag about a year ago and iPhone got a good soaking. She got it too work with the old bag of rice treatment, but the screen was permanently damaged.

Last week I inherited said iPhone which is still working perfectly minus corroded volume buttons and aforementioned screen. After scolding her for never doing a proper clean and dry of the phone, I take it upon myself to carry out screen repair.

I fully dissasemble the phone cleaning all the components with 99.7% alcohol. After they are dry I reassemble phone complete with new screen.

Moment of truth and I try to turn phone on, but nothing. No picture, no sound, no vibration. It doesn't seem to be charging but but with no physical feedback how can I one tell? Phone is a brick.

Open phone up again, check connections, no missing screws. Still no response from the phone.

So where do I start? Only ideas I have is to dissasemble and try again? And maybe by myself a decent multimeter, any suggestions?

Any advice greatly appreciated and will make me look less of an idiot for not just settling for a iPhone with a broken screen...