sleep/wake button doesn't work/ apps just loop when tryin to download

i recently bought an ipad 4th gen (A1458) second hand and noticed the screen had been replaced. i should have checked it thoroughly but didnt since it was a steal. when i got home i noticed sleep/wake didnt function like it supposed to but if i hold the power button i can still turn it off and the most weird thing i cant install any apps on to it i can live without the sleep/wake issue but why cant i install any apps i just get the loop as if to download but nothing happens.