Dell Studio One "Sleep" mode

I'm having issues with my All-in-one Studio One.  Most of the time it will not go into the sleep mode in the time I have set for it to do it.  Then, sometimes it does go into "Sleep" but I can't arouse it!  If I move the mouse or hit the power button for a second, it will show the start up screen for a couple of seconds and then go blank.  However, something is going on in the background because I can here the Windows sounds going on.  But no screen!  In order to get the screen again, I have to hard shut off the computer and restart it.  It goes through the entire Windows 7 startup process and then starts working.  I can't imagine that it is good to be doing a hard shutdown and restart nearly every time it goes to "Sleep".  Nor do I like to have the screen going through my "pictures" file for hours because it won't go into "sleep".  Something is wrong but what?