Does anyone know the temperature ranges one can expect on a core2 duo

The max case temperature is 72.4C. The processor itself will likely be hotter than that. (source: http://processorfinder.intel.com/details.aspx?sSpec=SLB9L#).

If your software is reporting a core temp of 50C you should be fine.

If you have added additional hard drives, a beefier video card or more power thirsty RAM, it may be that your power supply is too small (too low wattage). Other potential causes are bad sticks of RAM.

Intel lists this processor's Thermal Specification as 72.4, here: http://processorfinder.intel.com/details.aspx?sSpec=SLAPK#.

I've heard a rule of thumb "keep it under 75C". Most processors should operate perfectly at 50C.

I don't know the actual range for this CPU, but in general, I doubt temperature is your problem.

50°C is far from being a high temperature for a CPU, it's rather a normal one (for a small activity). As comparison, my T7400, in my laptop, can spike to 80-85°C without the computer to reboot (ok, it might reboot at 85...). It's a laptop, and a different CPU, but that gives an idea of the range.

So or the issue is not the temperature, or your CPU temperature probe has a problem, in my opinion (rather the first choice).