Here, I'll show you the site (normally you can't see this page without making an account):
I picked a random car to show the whole page. Usually, a customer would call in, and if they ask about a part, the receptionist can click the orange 'quick labor lookup' button on the left, and a window will open where you can enter more information. That button, along with the 'find it' buttons under each item in the picture above, no longer open a window. I looked at the browser options, and pop-ups aren't blocked, so I decided it was the antivirus. I uninstalled AVG Free, and lo and behold, the buttons worked again!
Unfortunately, they stopped working again after I installed Avast! Antivirus. I tried disabling Avast, but the buttons are still broken.