Garbled Graphics NES

I have an NES since 19 years and was shelfed for like 15-16 years, then I reconnected it 2 years ago and I was surprised that everything was working fine, even the duck hunt gun was working correctly, I was testing all of my 25 games in order to sell them and apparently all worked fine (I had a hard time in some of them but got all of them to work). But oh well, I only had luck selling like 3 of the catridges so I boxed my console again.

3 days ago, I tried to reconnect it again and found out that none of the games were working, I was getting the red blinking light on the NES. I know that blowing into catridges is a bad idea because you can spit into them accidentally and would get worse, but I did it very carefully and finally got them to work but with garbled graphics and it's really a pain, when the game is inserted I need to wiggle them and when I finally get an image I hit the reset button and it works fine at the beginning, but when the games starts to play more content, they start to display garbled graphics and finally get to a point where the game freezes.

I lent two of my games to a friend in order to test them on a different console, but in this case, it's worse because the games don't even load, even if I blow or wiggle the catridge.

So I really don't know if it's an issue from the NES or from the games, but I really doubt that all of the 20 games are having issues. What do you think it could be?