Ok - Since you have a wireless mouse, we can use Dell's drivers to disable to touchpad when your mouse is connect - when it is not, it will re-enable. Or disable completely through this route.
Note: If you do not see this Dell configuration on your laptop - you will need to download & install the driver on the link below.
To do this:
Go to the Control Panel. Under the ‘Hardware and Sound’ options, click ‘Mouse’
Since you have a Dell laptop, you’ll have a special tab called ‘Dell touchpad’ in the window that pops up. Click on the touchpad picture in the window.
In the new window that appears, click ‘Device Select’
Click on the ‘Disable’ radio button to disable the touchpad completely. If you want to disable the touchpad of your Dell laptop only when an external device like a mouse is attached, check the last option that says ‘Disable Touchpad/Pointing Stick when external USB mouse is present’
That’s it. You’ve disabled your laptop’s touchpad for good. If you don’t find an option to manage your touchpad in Mouse settings, you have to install Synaptics drivers from here