Google Play Store app doesn't work.

I've tried any possible thing to work again the Google play store . even reset to factory setting my lenovo tablet.but the problem still exist. What could be the reason for all of this?
 
My Samsung Galaxy ace 2 used to have the message when I opened an app description on google play "process.android.vending has stopped working". After doing a factory reset, for a while I was able to open google play, but now I tap on the icon, the google play takes a while to open, then all I see on google play is a black screen (with notifications on top). (The google play self-updated after first launch)
 
i got a similar issue, my apps won't start downloading, until i turn off the wifi & restart it back again