Check your BIOS settings. Then go from there. Be sure to check power options and verify Standby and hibernate (if you use hibernate) are enabled. If these options don't work, try updating your BIOS. Your vendor should have these updates. Also, check to see if your PC uses APM or ACPI. Hope this helps. If not, please include your hardware specs in your follow up.
Somehow, my system no longer has the Standby option. Any ideas?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic