In all of your dropdown combo boxes you have hard coded the background color to white. This is fine. However, you forgot to hard code the forground/text color to black. My OS Theme uses white text so I have white on white and cannot see what is in the list. Funny thing about this is that the Sound tab is correct. That one you did hard code the text color. Could you please hard code the text color to something dark wherever you hard coded the background color in the dropdowns to something light. Thank you!!!
In the below picture the highlight works because that is using all the windows colors and it runs inversed so you can see the one item I have highlighted.