Computer cannot enter sleep mode

[ryan29121]

I have a computer with vista and it cannot enter into sleep mode even though I have it set at 20 minutes. I even have to monitor set to shut off every 10 minutes but it doesn't even do that. The only thing it will do is enter into screen saver. My guess is that its the monitor causing it not to enter into sleep mode. My monitor is a 24" samsung 245bw. Thanks in advance for your help.