This guide is not exactly for your model, but it will probably work on your model, too:
Turn on safe mode
- Turn device off.
- Press power button.
- When the "Acer" logo is displayed, release the power button.
- Immediately after releasing the power buton, hold the volume down button.
- Keep holding down the volume down button until the phone finishes rebooting.
- Release the volume down button when you see
Safe Mode
appear in the lower left corner of the screen.
Source: http://howtosafemode.com/843/how-to-turn-on-safe-mode-on-acer-iconia-tab-7-a1-713?show=845#a845