Macbook Pro will not run on AC Power

Hi guys. I've got a MacBookPro5,1 model.

What it's doing (and not doing):
--When I close my laptop it shuts off, when I reopen it I can push the power button and go to a screen with a progress bar and wait to have my last session reloaded (this has been the case for the last year)
--Lately when I close it, it shuts off and I do not even have the option to regain my last session - it just reboots completely
--Also lately my mac has been shutting off randomly when unplugged (no matter what the battery life) - sometimes when bumped, other times not.
--It has also been shutting off occasionally when plugged in when I unplug a headphone jack, a usb cord, the power cord, or start a game in Counterstrike (not consistently though)
--It will not run on AC power alone (without the battery), but WILL charge the battery and will only boot from a dead battery after it has been charged for about 10 minutes

Damage Done:
My mac is 2 years old and has endured some rough times. It has been dropped twice and has 2 visible dents, one in the upper right hand corner (by the power button) and one in the lower left hand corner (by the internal battery connector). Also 2 summers ago I spilled a bit of melted ice cream into the superdrive rendering it useless. (I know. Smooth.) My problems are most likely connected to one (or all) of these mishaps, but I want to try and figure out what exactly is failing myself before giving up and having to hand it over to the Apple money vacuum. I'm praying it's not the Logic Board.

The fact that it won't run on AC power but will charge the battery makes me think it's not the battery.

Any help would be much appreciated guys. Thanks.

I would guess this is a problem with the DC board not providing power correctly to the logic board. I would defiantly get a second opinion before replacing it but they can be had fairly cheaply.

Not sure if this is the right one but it would be something similar.

Thank you for your reply thurstmw. That seems to make sense, but do you think that problem would have anything to do with the laptop's shutting off when things like headphones are unplugged?

freddcow said:

Thank you for your reply thurstmw. That seems to make sense, but do you think that problem would have anything to do with the laptop's shutting off when things like headphones are unplugged?

Click to expand...

Oh I missed that one... I doubt it. Hopefully when you are doing that it is just bumping the power cord enough kill it because of the DC board.

I would personally try cleaning the logic board with alcohol but that is not really something that most people are willing to try. If you are comfortable taking the computer apart though you could at least take out the logic board and give it a visual inspection to see if there is any corrosion ect...