Mesmerize Won't Boot

I still use a Samsung Mesmerize (US Cellular) because it allows me to tether. Finally the charging port went bad, so here's what I did..

I bought another Mesmerize - nice phone - from the original owner - original box etc. - not a mark on it. It powered up fine and booted to the home screen. So for the past few days I've been using this new phone to charge batteries.

This coming week I planned to have the 'new' phone activated and then make my original phone my backup. (I have the new charging port part and planned to replace that)

Problem is.. all of a sudden this 'new' phone won't boot. All I was doing was charging batteries in it - and all of a sudden when I put in a battery I was not getting the battery-charge icon with the green graphic. (Just the battery icon but 'before' it indicates charging)

So I decided to power the phone on. It comes up with the SAMSUNG logo but that's it. Never goes thru the little fanfare and splash page. Just sits there mute.

I tried to get it into recovery mode by holding down the volume and power buttons but no dice. Just comes up with SAMSUNG and that's it.

Any of you guys have any ideas on what else I can try?