How do you launch Starcraft? Are you using a desktop icon?
If you ever tried playing around with the shortcuts to get it into windowed mode or something, the shortcut path may have been altered.
If you're using the auto-launch menu when you insert the CD, then it's something else, possibly a setting from your video card that's causing that.
If you're using a shortcut, right-click on it, go to Properties, and look at the end of the path in the "Target" path if there's any extensions after "C:\Program Files\Starcraft\starcraft.exe"
Otherwise try reinstalling your video drivers. I'm out of ideas after that point.