PCB contacts for membrane keyboard looks corroded?
Clean it as Tony suggests (pink or non-abrasive white eraser) and it looks like you got water into it. Don't do that. Maybe the water got in deeper and damaged something else - you should check that out. IPA alone should have cleaned it (assuming it is proper high purity isopropanol and not drugstore rubbing alcohol which is adulterated with additives). 

Do NOT sand it as you will destroy the super-thin layer of gold plating on the contacts and it will never be reliable again.