Quick explanation of "S" Modes S0 (Working) is lit. The CPU functions in entirety; the conservation of power is on a basis of by-device. S1 (Sleep). The CPU is stopped; The RAM is regenerated; the system functions in reduced power. S2 (Sleep 2) The CPU does not have any power; The RAM is regenerated; the system is in lower mode of the S1. S3 (Standby) The CPU does not have any power; The RAM regenerates at minimum; the power supply unit is in mode of reduced power. This mode is also called “Save to RAM”. S4 (Hibernate). All is powered off, but the memory was saved like temporary file on the hard drive. This mode is called “Save to disk”. S5 (Off) Everything is shutdown. Means you need a full reboot. S3 is the best. It uses less power and reboots faster. Vista and Win 7 have hybrid sleep. If you are having issues with your PC waking on it's own and You have already exhausted all the BIOS options and your getting annoyed try this simple solution. In the Windows Vista or Windows 7 start menu type: CMD and select the command prompt On the Command line type: powercfg -lastwake You will get a short list of your wake history at the bottom look for the Friendly Name such as Reatek PCIe GBE Family Controller Then go to Device Manager through Control Panel> System and Security> Sub menu SYSTEM and then select Device Manager. In Device Manager find the device listed under the Friendly Name from the command prompt. In this case Reatek PCIe GBE Family Controller would be found under Network Adapters Highlight the device by left clicking on it once and then Right Click and select Properties. In the Properties tab Select the Power Management Tab and make sure that the Allow the computer to turn off this device to save power is checked. and make sure that the Allow this device to wake the computer IS NOT CHECKED . Click OK and this will hopefully solve your Sleep issues. More advanced solutions If you've made a hardware change such as a GFX or Mobo Remove Ghost Hardware: Open CMD as Administrator Type or Copy Pasta SET DEVMGR_SHOW_NONPRESENT_DEVICES=1 Then start Device Manager by typing: devmgmt.msc Then in "View" click "Show Hidden Devices" Click on the device tab and remove the "Ghosted" Hardware....It will be the gray translucent device Do Not Uninstall the Device Software Unless you are 100% you don't need it... Example: You changed motherboards and your previous board had "VIA HD Audio" and your new Motherboard has "RealTek HD Audio". Not every Ghost needs removed as some items are simply the same devices such as a Keyboard on another USB etc... Run cCleaner Remove unwanted software and Run the Registry Cleaner only after you understand what could happen and have taken the correct precautions.