|If Windows does not have the proper information about how the ACPI features of the mboard are supported, which include how Standby, Hibernate, wake on .....features and sometimes Restart are supported, those features may not work properly until AFTER you have installed the main chipset drivers for your mboard, which include that ACPI information.|
Whenever you load Windows from a regular Windows CD (or DVD) from scratch, after Setup is finished you must load the drivers for the mboard, particularly the main chipset drivers, in order for Windows to have the proper drivers for and information about your mboard hardware, including it's AGP or PCI-E, ACPI, USB 2.0 if it has it, and hard drive controller support. If you have a generic system and have the CD that came with the mboard, all the necessary drivers are on it. If you load drivers from the web, brand name system builders and mboard makers often DO NOT have the main chipset drivers listed in the downloads for your model - in that case you must go to the maker of the main chipset's web site, get the drivers, and load them.
If that doesn't help for Windows 7, if your mboard is older, it may not be compatible with Windows 7's support of ACPI features.
If you still have the problem when the main chipset drivers have been loaded in XP, there is something else wrong.
A poor connection of the ram in it's slot(s).
A defective power supply.
If the mboard is not new, e.g. it's at least, say, two years old, you may have the failing electrolytic capacitor problem on the mboard.