No video signal found

Turn PlayStation on HDMI hooked up properly but won't find a signal tried video reset but the system just shuts off I'm not getting any yellow light just the red when off green when on so it shouldn't be an overheating problem. It is an older system but it's not a slim is my son's and he wanted me to try to fix it I open it up for the fans didn't seem like they were running properly and it was full of dust I clean it up the best I could