windows 7 - Erratic Mouse Click buttons, on Laptop and with External Mouse

On a Dell Inspiron laptop, the mouse buttons are sporadically erratic, either not working, both buttons working as a left click, etc. This also happens when you use an external mouse, so it's not the physical keyboard. Have run AVG and Malwarebytes, no problems found.

This laptop was shipped with Vista, with a free upgrade to Windows 7. I've been unable to find a cure, so I'm planning on wiping the computer clean and reinstalling Windows 7. I know the general process, but I have two concerns:

1. The laptop does not have a CD drive, you have to use a USB external. After formatting, is the USB CD drive going to be recognized? If not, how to I get around this?
2. Since it's an upgrade, I'm concerned that the Windows 7 will not install unless it sees an existing copy of Vista. I think the original Vista is part of the problem. Any suggestions?

Don't start with the reformat. Connect the DVD drive, put in the DVD, and try to boot the computer from the DVD first. Once you've worked that out, the Windows Installer will offer to format your drive for you, and you can be sure that you can access the DVD drive by this point.

To your second question, a quick Google uncovered this page: Clean Install with a Upgrade Windows 7 Version