|"The SM Bus controller in device manager has a yellow '?' by it."|
Try Uninstalling that entry and rebooting, then looking there again. If it still has a yellow ? beside it, or in ANY case....
Windows may not have the proper information about your motherboard chipset's ACPI support, which determines how Shut Down, Standby, Restart and other ACPI related things work, if you have not loaded the drivers for the main chipset, or if the drivers and/or the ACPI information have/has become corrupted.
(The SM Bus controller problem may not be directly related to your problem, but if it is not recognized properly that often indicates the main chipset drivers have not been loaded or are corrupted.)
If you still have the brand name maker's original software installtion on your computer, the proper mboard drivers are already present, and you should NOT be getting that SM Bus controller error, and your ACPI features should work correctly, unless something has become corrupted.
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, 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.
In your case, you have the Intel 855GM chipset.
The main chipset drivers and/or the information Windows needs about the mboard's main chipset are loaded by you downloading and running the INF Update Utility here:
If you're not sure whether the main chipset drivers are loaded, or they have been but you're not sure whether they may have become corrupted, it does no harm to try loading them again, and you usually don't need to un-install main chipset drivers before loading them again.