I've had my system overclocked for 4 years now, everything has been stable until about a year ago. The system will freeze anywhere from 1-5 hours of being on. Also, when frozen, the sound will be 'buzzing'.
For now I will attach screenshots of CPU-Z so you can see about the mem/cpu voltages and clocks.
Might take a bit of trial and error to get this one sorted. I seem to think it could be a memory issue, perhaps the clock OR voltages. FYI: I increased my CPU clock from 2.8ghz to 3.5ghz, I didnt' actually do any overclocking on the ram. I understand that if you overclock the FSB or CPU that you will need to tweak the ram, too?
Are you getting blue screens? If so, it sounds like maybe it's an unstable overclock. Put everything back to stock and see if you have any freezes or lock ups. Also, RAM should be the last thing overclocked. Overclock the cpu first and once that's stable then work on overclocking RAM.
the freezing combined with the buzzing makes me think that your psu is failing, and is thus, undervolting the cpu. when the cpu undervolts, it causes freezes, when the ram undervolts, it causes bluescreens. you have 2 choices, get a better power supply or raise the cpu voltage.