Hi, I've Overclock my E6300 to 2.8GHZ without any issue for 2 years until now. When I've able to pass POST with that speed, I ran Orthos for 12 hours stable. When I Restart, The PC cannot boot up and the LCD show a blinking power light. The only way to boot up is to turn off the PC for a few minutes and the PC will boot with it's default settings.

The issue is even If I OC by 2.0GHZ, I've still experience the same thing, Only stock speed have no issue.

Using F14 Bios.

My Spec.

E6300 1.8GHZ
5850
2GB DDR667 Value Ram
450W PSU True Power

psu might be the problem

Anyway, do check out with the following:

1) Try with another PSU
2) Check your rams, clean the connectors. ( yes it happens)
3) Check your peripherals, clean their connectors.

Then post back here.

Is that a new HD5850? Running on a mere 450W PSU? Tell me what brand/model is that PSU?

Note: For HD5850, its recommended to use (at least) a true power 500W PSU and higher (preferable).