If I were in this situation, based on the limited information supplied, the first thing I would try would be using Windows System Restore to restore my system to an earlier time.
If that failed to resolve the issue, I would undo the restore, so the system was back at the current state. I would then uninstall the current touchpad driver from "Control Panel - Uninstall a program" and REBOOT, letting Windows 7 install its Plug-N-Play touchpad driver. I would confirm the touchpad buttons work properly with this driver.
If they worked correctly, I would then install the latest touchpad driver for the specific brand of touchpad installed on the system.
If the above failed to resolve the issue, I would perform an ASUS Factory Restore, choosing to restore Windows to the 1st Partition. Be sure to backup any important files on this partition because it will be completely overwritten.
If the issue still occurred, I would contact my retailer and ask to exchange the laptop for a new unit. If I was outside the retailer's exchange/return period, I would RMA the laptop for warranty repair.
G74SX-A1 - stock hardware - BIOS 202 - 2nd Monitor VISIO VF551XVT