My Pokemon Sapphire GBA won't load passed the Nintendo screen. Any advise?

I purchased an authentic copy of Pokemon Sapphire for my GBA. The seller told me it wasn’t powering on correctly but he believed it was a cleaning issue. When I received it, it booted it up and it was doing exactly as he described. The GBA logo appears but the Nintendo logo is scrambled. I opened it up and cleaned the whole board but it wasnt all that dirty. I checked the continuity on all pins and they all seemed to be reading. I am currently at a dead end. Can anyone help?