Go to Acer's website and install the latest drivers for the touchpad. Reboot after installation.
If that doesn't work, check to see if the touchpad is detected in Device Manager (it should be listed under "Mice and other pointing devices").
If it's not detected, the cable that connects your touchpad to the motherboard might have come loose. Do a quick search and you will find videos that will walk you through removing the keyboard so that you can re-attach the cable.