Overclocking not sticking?

[JLCollier2005]

Hi all, I've recently started to over clock my computer and I've tried twice with weird results. Both times CPU-Z said it was up to 2.0ghz, but as soon as I reset, it goes back down to 1.8ghz. Anyone have any idea why? I'm using AMD Overdrive, but am willing to go into the bios if needed. I'm just not that experienced.

My system is...

AMD Phenom X4 9100e @ 1.8ghz
Gigabyte GA-MA790GP-UD4H mobo
4gigs of ram
Radeon HD 4850