I cannot connect to wifi on Samsung tab3, stays grey not green

Reset to factory settings or stay in Wifi zone... choice is yours

What kind of tablet is it?

Try a factory reset Samsung Galaxy Tab 10 5 Hard Reset Factory Reset

you may have to reset it to factory settings to sort it out, sounds like some tyke has change it as a joke?

this may be because they wifi goes away and comes back again. or maybe because it's messed up .
hope this helps.

the problem is in the wifi. The network is unstable

Go to applications, settings, back up and reset. If you want to save your data check the "back up my data" box, then tap the "factory data reset" and tap the "reset tablet" tab. The tablet will then be reset to the original factory settings.

You may have to reset the tablet to factory settings. This may be the only way. It will wipe all the data on it.
To factory reset:
1. Press and hold power plus volume up until an android menu appear 2. Use the volume keys to navigate and option key or power to select. 3. look for factory reset and wipe data 5. restart the device and it should be back to factory settings.

Reset router, and try again, if not reset to factory setting's..

When you reset the tablet your tablet wifi settings, wifi name and password will be erased. You have to detect your wifi on the tablet, connect to it and enter password right?