I'm a new user of Adobe, and I've been experimenting with After Effects for a couple of days. Everything was working fine until suddenly, the preview stopped playing halfway through this project. At first, there was a red vertical line (which I assume goes to where it rendered?), but then after I deleted the spacebar shortcut and remapped it to Preview again, nothing happens when I click the spacebar. I'm not familiar with the interface or names of things so I haven't been able to find any answers online; in addition, I'm not very familiar with computers in general. Does anyone know how to fix this so that the preview video plays and the timeline indicator moves in real time?
You have a full-resolution HD comp that is about 30 seconds long. It is not going to reliably preview the entire 30 seconds. AE is complicated, it is not a video editing app, it is not designed to edit. If you want to efficiently get a handle on the workflow and develop good habits please start with the tutorials in the User Guide and avoid tutorials on YouTube prepared by enthusiasts that either poorly explain or demonstrate inefficient and sometimes downright wrong workflows. Vet your trainers and spend some time learning how AE works.
If AE completely stopped responding and Purging all memory and disk cache does not solve the problem try a reboot. Make sure your system meets the minimum system requirements, and make sure you are on the latest build of your version of AE. If you still have problems we need workflow, OS, system, and AE version details to point you to a solution.