Windows media center has changed my systems standby behavior. How can I change it back?

When I used media center to record a series of tv programs, it changed the system standby so that the system doesn't really stand by. Instead the screen goes blank but the system keeps running (for example, outlook still fetches emails, scheduled programs continue to run, etc.) I think I've canceled the series recording, but my system hasn't reverted to its previous normal standby behavior. (When it sleeps, I want it to keep sleeping until I wake it up, the way it used to operate. Not have it wake up automatically to check for email, etc. like it does now.) Is there some straightforward way to change it back?