May be it just takes a really long time ? I've noticed that it can take as long as 2 minutes at times to launch the app on the emulator. When in doubt use the 'Clean app data' check box on the emulator to clean application state. That helps sometimes.
I've had the same problem sometimes. I've experienced that you've got a better chance that it will work when you first click on your project name (most upper file) in the Package Explorer (assuming you use Eclipse!) and than run the emulator.