5850 Flashing/Vertical Flashes when I try to OC

[teldara]

Anyone have the same problem? I tried over clocking the 5850 and it just starts flashing and vertical lines appear.

Even if I go 1mhz above default, it does this. Is there a fix?
I read somewhere that it switches between 400Mhz to 725Mhz (my default I think) and it keeps making those lines.

Or do I have a defective card?

I'm running a dual monitor setup.

 

[buwish]

I've read that the 5K series are pretty overclocking averse. Are you using the catalyst control center to do so or Riva Tuner? However, it could be a defective card, as even though they aren't too keen on overclocking (the 5k series), I've gotten my 5830 up 100Mhz on both the core and memory without any issue (but that's as far as I can get it to go without crashing it using RivaTuner).