Spoke to soon. Well that's odd. It seemed fixed and worked great for the few minutes I was playing it. Came back to test again and the problem is back.

Update: Swapped the contrast wheel and all is fine now for sure.

Reflowing the solder on the rails and the contrast wheel worked! Which one fixed it I don't know. I should have isolated it so I could potentially help others. Alas, I'm an idiot and only think about those things after I'm done. Thanks everyone!

Probably not the cause. Im guessing it is the discrete components dying on us. Capacitors leaking/drying up, resistor values drifting over time, etc. 
We need a modern power board replacement.

I'll go in and reflow the solder around there too then.

If the negative rail coming from your power regulator board is not constant, it could cause those problems I think. I am hearing about gameboy power issues more and more lately.

Nope. Still doing it. Could probably scavenge a contrast wheel and do a swap. I'd rather not though. I'm hoping someone has some ideas before I have to resort to that.

Not brand new. Practically new though. They are my test batteries. Meaning I only put them in to test if a system turns on then I take them out. I just opened them last week too. I will try to find some new ones and get back to you though. Thanks for your time!

this is probably a stupid question, but are the batteries brand new?

I just received a DMG that would not turn on. I cleaned the contacts and guess what? It turned on! If only people would check them before trashing them. It now has another problem though. The contrast flickers like crazy. No matter how you adjust the wheel the contrast just gets dark and then lighter in a loop constantly. It works great. I can tell the screen works when I put a game in but the constant adjustment of the contrast makes it unusable. Any idea how I can fix it? I'd hate to throw this one in the parts box too. Thanks in advance!