Pitch Black Screens on my DS Lite: Solid Green Light Remains

In the past year, I began to revisit my DS Lite. I had not used in over four years and it failed to turn on at first. However, I temporarily fixed the problem by hitting the DS again the butt of my palm. The problem reappeared and I realized that if it pressed hard on the bottom left corner of the screen the DS would freeze. The problem continued to occur but I solved it each time by hitting the bottom of the DS under that corner of the screen. Unfortunately, I recently broke the power button on the same DS and had to open it up to remove the switch. I turned it back on, hit it a few times and Voila, it was working fine for about ten minutes. Now, my previously effective method is not working and I cannot find anything amiss inside the DS. Any suggestions?

P. S. Don't just say "buy a new one"