sleep mode not working all

I have tried for 2 days to get my system to go into sleep mode with no luck. It will turn my monitor off but the harddrive light flashes every 3 or 4 seconds and all the case fans keep running. I have messed with all of the advance power options and nothing seems to work. This is a custom built desktop rig. Any suggestions on what I could try to get this thing sleeping properly? I actually believe that it worked before I setup the media center portion of Vista. Any help is appreciated. Thanks

I have been trying for two days to get the sleep mode to work with my system. I am running a custom built desktop. My monitor will power off but the harddrive light will flash every few seconds and all of the case fans are running. I am 99% sure that the sleep mode was working before I setup media center. Once I set it up is when I noticed the sleep mode stop working. I have messed with all of the advanced power settings with no luck. Any ideas? Any help will be greatly appreciated. Thanks