need help - mobo won't let me change the voltage settings

I'm trying to increase the voltage to my CPU (unlocking the last core on a Phenom II X3) but it's grayed out in the BIOS. I even tried doing it through windows w/ AMD OverDrive, but it just won't change. Is it simply impossible to do on certain motherboards? Would the BIOS determine that? Is there any workaround? ANd why would the motherboard maker lock that option?

my mobo, in case anyone was wondering

Check the manual for anything on the OC switch. See if it might lock out overclocking options if some kind of setting is activated on it.
-----------
Okay, just looked over the manual and nothing on the OC switch would do that. I'm looking at BIOS options right now as well and so far I'm not finding anything on way the voltages are locked out.
-----------
I looked over the forums and the manual and I'm not finding anything useful. Mods on the MSI forums are saying trying to use Page Up and Down, but I don't know if that'll work.

Check the manual for anything on the OC switch. See if it might lock out overclocking options if some kind of setting is activated on it.
-----------
Okay, just looked over the manual and nothing on the OC switch would do that. I'm looking at BIOS options right now as well and so far I'm not finding anything on way the voltages are locked out.
-----------
I looked over the forums and the manual and I'm not finding anything useful. Mods on the MSI forums are saying trying to use Page Up and Down, but I don't know if that'll work.

kilerchese