Something as simple as a complete reset of the application can solve simple issues, have you tried it?
Here is how you can reset the preferences:
PressAlt (Windows) or Option (Mac OS)while launching After Effects. You can release theAlt or Optionkey when the splash screen appears.
To reset preferences and plug-in cache at the same time, hold downControl-Shift-Alt (Windows) or Command-Shift-Option (Mac OS)while the application is starting. Release the keys when the splash screen appears.
You said you've tried "everything," but didn't specify, so we can only make guesses here.
Byron's suggestion of resetting preferences is the first thing I'd recommend.
Tried importing this project into a new, empty project?
Have you tried opening this on another machine, or sent it to a friend to try this?
You said it crashes when you try to change something on the timeline. Can you safely navigate in the Project Panel? If so, you may be able to split this project into smaller pieces (using File > Dependencies > Reduce Project, and make sure to "Save As" so you don't lose your original!). This may help you figure out if there's a single problematic composition, or a larger systemic issue.
Are you getting the crash pop-up that allows you to submit a crash report to Adobe? Similarly, if you activate logging (Help > Enable Logging), AE will generate a log of events, that an Adobe team member may be able to get more info from, if none of the above has helped.