Will I have to reset my Nexus 7? I have a Nexus 7 running Jelly Bean. I was downloading a file and somehow I managed to remove a tick mark some were. Now I can not download anything from the net without Chrome stops working. Then I tried to download a backup program from Play Store, that mad Play store stop.

How and where do I add the tickmark again? Will I have to reset my Nexus 7? If so are all the app I bought then lost?
If youre talking about applications (.apk) downloaded from google chrome and not the play store then you need to go into Settings > Security > Unknown Sources