Hi,
Try a "hard" reset on your tablet.
Before you do, perform a '''backup of your data''' as'' a hard reset will erase all downloaded apps and user data.''
Here is a link that shows you where to go in the tab to perform a back up / factory data (hard) reset. Scroll down to the''' 2nd Method''' shown in the link. '''Remember to do a backup first.'''
http://www.hardreset.info/devices/acer/acer-a1-830-iconia-tab-8/