Hd 5770 OC problem? Helpp?

Hello I just got a new CPU so I can use my hd 5770 at max. (now my Gpu is the bottleneck in my system) but I want to overclock my Gpu to get a little more out of it and it runs very cool Oc 932 core 1300 mem. Use furmark for a hour never goes above 73c. In games it hits 63 and that's max. So I wanted to see what 960 core 1400mem max on settings msi afterburner. So I turn on furmark and the video card shuts off and about 30 secs it comes back on.

So just wondering if that's a problem with a card. Or is my card just saying NO. Eny ideas.

Specs

Windows 7 64

Intel i3 2100

DDR 3 1333 4 gb

HD 5770 xfx

350 gb hard drive

500 w psu

And a case fan. Ya|||Obviously, that means you've overclocked *way* further than the card can go. I also don't recommend overclocking both the core and the mem at the same time when you're first testing possible overclocks. Only combine core and mem overclocks after you know each one works alone.