My starmobile android tablet Engage 8 lags so much?

My starmobile android tablet Engage 8 it's too long to open than before then if it's opened it will work like 10 secs. then it lags so much you can't even use it any more, I was just about to play NBA 2k13 then it lags so much then i turned it off then charged the opens it again and it lags so much and lost my apps..... what could be the problem?..... sometimes there a message popping up system UI not responding what is that?