Sleep doesn't sleep anymore - just goes to login screen

For some reason, my 'sleep' has stopped working - either from the sleep button, or on the Start button option.
Now it just goes to the user login screen.
Has always worked perefctly until today.
Weird. Any ideas?

imaken

You might want to try the same tutorial as last time Power Options and Sleep Mode Problems - Vista Forums

Ken

Again, you've come to the rescue!
That cured it - thanks a lot.