Android tablet was working now all apps says app isnt installed

[krwash2]

My son's Android tablet was working great. Now when i click on ay play store apps, I downloaded they say app isnt installed. I have uninstalled and reinstalled and they still dont work. My other son's is working fie with no issues. Please help.

 

[Rukbat]

Application Manager. Google Play Services and Google Play Store. Clear cache. Clear data.