How to Disable Touchpad in Windows 7: Turn Off Your Laptop’s Internal Mouse
Step 1: Click the Start button on your computer screen (bottom left corner), then type main.cpl in the search box. When you are finished typing, click Enter on your keyboard.
Step 2: In the new window that opens, click the Device Settings tab at the top. It should be the last one on the right.
Step 3: While in the Device Settings section, make sure the name of your touchpad is highlighted (it should be already), then click the Disable button. Click OK, then click OK again when the warning box pops up.
That’s it. Now, whenever you have an external mouse plugged in, your touchpad will automatically turn off. A simple solution for a gets-old-quick problem.
Step 4: If you’re still having trouble disabling your laptop’s touchpad, you might need to download a new driver. Try this link for Synaptics Drivers. You could also download and install the TouchFreeze program (you must be signed in with Google to download), which turns off the touchpad while typing.