My laptop is 3 months old and the pad has just stopped working,can you help?

SOURCE: touch pad

Check the state of the batterie , take it of and put it back on sometimes this will solve your problem ( bad batterie state )

SOURCE: Touch pad stopped working

I recommend you to uninstall and reinstall touchpad drivers to isolate the issue.
Press Windows key and R. Type devmgmt.msc in Run window and click on OK. Click on "+" sign beside Mice and other pointing devices in Device Manager.
Right click on Touchpad and select Uninstall.
You will be prompted to restart the computer.
Windows detects touchpad and the touchpad drivers will be reinstalled automatically.
You can also install touchpad drivers from your notebook support website.
You can reinstall the drivers from the below links:
http://support.acer-euro.com/drivers/notebook/as_5920.html
http://www.laptops-drivers.com/acer-notebooks/download-drivers-acer-aspire-5920-notebooks.html
However I suggest you to install the drivers by visiting the acer support website.
Also perform windows update.