CS5 is unsupported under Windows 8.1. The first thing to do is make sure you're running the laptop at 100% for the UI and at the native resolution of the screen.
What's bizar is that other applications work perfectly fine at the right resoution (like photoshop CS5 for example). The screen runs at its native resolution. The rest of the program works "fine" (except its uglyness because it somehow doesn't display in 1920x1080 even though that are the native settings of the screen.)
What do you mean exactly by running the laptop at 100% for the UI? I did not use any other programs and the laptop is brandnew. Actually CS5 is the first application I installed...
So, you didn’t set anything in the UI for large fonts or anything like that? Like I said, it’s unsupported so I’m afraid you’re on your own.
Perhaps someone who has CS5 running well on 8.1 can help.