Does the LogCat or the Console have any errors or warnings?
There is always the possibility that you didn't set your project up to be compatible with the Emulator's Android Version that you selected, but I'm not sure what would happen if that was the case.
How long do you wait when you press "Run As..."? Keep in mind that the apk needs to be created and then it actually gets "installed" onto the Emulator so, depending on the size of your project, it might take a few seconds, or even a minute or two if you have a slow computer.