First of all you are to check if data connection is turned on.
1. Place your finger top right of your tablet screen and slide it down.
2.Touch "DATA CONNECTION" and select the required SIM card if you tablet is Dual SIM.
3. Repeat step one again
4. Touch Settings.
5. Touch Apps.
6. Under "Downloaded" Look for "Google plays store" and then open it' if not under downloaded then go to all apps
7. Touch "Launch"
8. Type "Nova launcher" in the search bar. Nova should be first in the search results then install it.
9. You can use an app called LINK2SD to make Nova launcher a system app so that you wont get the same error after factory reset..
See another method here http://www.satechhelp.co.za/7948/Fix-Launcher-3-Stopped-Working-Android-Tablet