I've seen Vista work through every command by the user to shutdown/go to sleep/reboot, regardless of whether the powers been cut. If you hit the sleep button more than once it might very well go to sleep for each time you pressed it. Let it do its thing 2-3 more times. If you continue to get issues you may have ruined your install. Boot from a Vista DVD/our recovery disc and attempt startup repair.
In the future you may want to go to advanced power settings in the power properties in control panel and set the button to shutdown rather than sleep so it does as you had orginally wanted.