It's possible you may have pinched a cable or have a plug not correctly placed by the sounds of it. That is if you bought from a reliable source. I would reset all te plugs on the upper connections of the phone. Might be worth sitting the phone in rice for a day or two before in case there is still some water.
I curious as to the positioning of this gold metal piece also as I am having similar issues. I have a signal but only in strog areas and 3g and wifi are bouncing on and off effecting the signal. Im curious as i sat this piece in as i believe is correct but cant get a pic of it anywhere. They say there could be some grease on the attenna cable so might try cleaning this with alchol
This sounds like you got water or damaged the Doc connector where the charger plugs into so its not charging the battery so when you unplug it just dies straight away. replace the doc connector and take it from there as the battery is next in line! i got one for a fiver on ebay!!!
To me I think its the Doc connector. If this gets any water damage it turns kind of multicoloured(pink-green) if you replace this i expect it may solve it. If it doesnt then its the battery!! Problem is the battery wont charge so when you plug it out it dies!!