I fixed a problem but now got another one...somebody help?

Fixed blinking red light first but now as I power on the system, there's only snow and noise on the screen

Tried 2 different video cables (both quite old tough)

Cannot be the cartridges as each and every one got cleaned inside out by me.

It is related to the video/sound but I doubt on the connectors as I'd get nothing on screen/speakers if it were to be the case right?

Anyway if anyone can figure it out with this diagnosis I'd be more than thrilled^^"