How can I disable my laptop's built-in keyboard in Windows 7?

Look at this article, it will help you to disable your laptop keyboard by uninstalling your keyboard driver.

• Go to Start–>Search type in gpedit.msc
• Click the file to open the Local Group Policy Editor and show Windows who is in control!! You want to go here: Computer Configuration->Administrative Templates->System->Device Installation. Click on the subfolder Device Installation Restrictions on the left and on the right side you will see the possible restrictions.
• Right Click on Prevent Installation of Devices not described by other policy settings and edit this option, set it on ENABLED.
• Reboot Windows and enjoy its inability to pollute your system with its standard driver, open gpedit.msc again and revert the change so you will be able to install your driver.

For laptop Asus X82S using Windows XP, I was successful using these steps

Please go to C:\Windows\System32\Drivers\.... You will see some files start with kb, change kbfiltr to kbfiltr_del. And you will have done it.

This will disable laptop keyboard. At the moment, I use USB keyboard. And no problems for keys anymore.

I'm not familiar enough with this machine to tell you how easy it is, but generally the keyboard on a machine like this is end-user replaceable, so you could simply replace it. Alternatively, you could just open the machine and unplug the data cable connecting it to the motherboard. (I suggest this way specifically so that it doesn't cause you grief in the BIOS or something like that, if the occasion arises.)