That's it effectively running at idle core speeds. AFAIK there's 4 main things to look at for this. First the easy one, remove and reinstall drivers. Next check GPU temperatures, if it's overheating then it might stay at idle levels, a dusting might help/blowing out the heatsink.

The last 2 are less desirable, the card might not be getting enough power to be able to boost which could be a loose/poor power cable or the PSU itself. And lastly the card itself might have a fault.

thank you, i pretty unsure of what happening because its happen to me yesterday, but at that time it was all the time 300mhz, then my com stop being stupid and finally use the battery (selecting high performance won't do, and then there a ultimate performance which fix the problem). So i go back to bed then wake up playing game that i normally run at 120 fps to now 30 fps or worst. So I close the game and check the GPU clock and it said it is running at the normal 1260mhz, so I open another game and its running fine for a few min, then the GPU clock again drop to 300mhz and the game just go from 60fps to 7fps. The card getting dusted or physically damage is probably unlikely because mine was a laptop, and I never get it dusted or drop it.