Trouble Overclocking ATI 4870 in Catalyst

I am having trouble overclocking my ATI 4870 in the Catalyst Control Center. I tried overclocking it to the 700's mhz, but it says its current GPU is 500 mhz. The Memory clock, I can overclock it all the way up, but not the GPU clock. I dont know why my GPU is not overclocking, but I only have one idea and that is because I have a Gateway. I can't overclock my AMD 8400 Phenom processor which is only pushin 2.1 ghz. Any suggestions?????

Have you tried using Auto-Tune?

I've down clocked mine to 500/450 to keep my system cool, but Auto-Tune rated it to go up to 820/1175.