Once you reach the Level where Cloud Cuckoo Land is under attack, you may run in to the issue where the Abraham Lincoln NPC gets pushed off the map and after fixing his chair, nothing happens and you're stuck in a cutscene which never plays since the NPC fell off the map and doesn't get into the flying chair. The following steps in this guide will hopefully allow you to resolve this issue as this is how I resolved this issue for myself.

Most people are probably playing with the highest graphics settings, but to fix this you'll need to do the opposite. Start by going into your settings and turning your settings to 800x600. After you've done that, turn V-SYNC ON. You need to do this BEFORE GETTING TO THIS PART OF THE LEVEL. That's important or you may still have the glitch where he gets pushed off.

If doing that still doesn't work and won't let you keep going then try again. If after several attempts it still doesn't work then I don't know what else you can do. I'm writing this from personal experience and how I was able to beat the level and game 100%.