Okay, I have an old NES-001 that I opened cleaned it, and lifted the 72-pin thingy. It worked like BRAND NEW! I was so happy! I was playing Zelda II, The Magic of Scheherazade, and METAL GEAR. It worked last night too.
Today, I took the NES apart so I could give the CASE a nice paint job. I disconnected the controller ports from the mother board, (I got pictures) but not the 72-pin connector, ( I left that alone)

Put everything back together, and BAM! The same games I played last night, just go to a GREY SCREEN. (Not blinking)
My GF was so upset, and asked me what I did to the NES. I said NOTHING I just painted it!

Any suggestions on what to do? Feel free to ask questions.