The update may have caused a 'glitch' (do you like the highly technical term?) in the OS.
Try the following:
Backup all your data using the tab's backup facility. Also do a separate backup of your contacts and pictures just to be sure. Do this first before proceeding with the following. Also ensure that the battery is fully charged and that the SD Card (if installed) is removed. Do not leave the charger connected when performing a reset.
Then perform a factory reset on your tab. This will erase all your user data and downloaded apps and restore your tab to a factory default condition. That's why it is important that the backup is done first. Doing a factory (or hard reset) means it will revert back to the latest updated version, which is stored in your tab. Basically the OS will be re installed.
Here is a link to the section in the User Manual for your tab which shows how to do a backup and reset.
Once the tablet has been reset, ensure that it is stable and functioning correctly, (remember it is only the basic tablet now, like when you first bought it).
When satisfied that all is working OK use the restore option of the tablet to restore the tablet using the backup that you made earlier to restore it to how it was before you started all this.
The short version of all the above is backup > reset > restore.
Hopefully the 'glitch' will have been removed and all is back to normal.