You're probably correct--I'd guess it's a BIOS problem. You need to make sure that ACPI is enabled and that hibernate or standby is enabled.
For mine, it has been under the Power tab. Also, try changing it in the BIOS that when it receives the power button signal to enter hibernate.
If those don't work, find your mobo's manual online somewhere and link it or write down the options in your BIOS and post em here.