i presume its a barton 2500+ u have in there. 66C is a little on the higher side for a 2500+ unless its overclocked. Check if the heat sink is seated properly on the CPU. apply some therml paste such as Artic Silver 3 to make better contact between the CPU and the heat sink. And finally, which Volcano heatsink do u have there with u?
if that's the LOAD temp, then that's a bit hot for a Barton. not panic-stations hot, but a little warm all the same, especially as it'll have cooled down in the time it takes to reboot and go into the BIOS.
Exactly what heatsink are you using, and exactly how did you apply the thermal paste?
Also, have you used anything other than the BIOS to check your temps? it's possible it's just being misreported. you could try using Sisoft Sandra, or Motherboard Monitor 5.
$hit Happens. I just wish it would happen to someone else for a change.
Barton 2500 with stock cooler should not get above 50C. Must be bad airflow in your case. Try and stay below 60C and use some arctic silver 3 compound. Also I found bios gives a reading halfway between load and idle. If i go in bios now, i get 52C. Just running windows i get 50C and running prime95 i get 55C.
Edit: What are your voltages for cpu? If its above 1.65v then its too high for stock speeds.
I just built a computer with a barton 2500 and stock cooling with 1 case fan. both the bios and pc alert showed the cpu temp at around 30 c/84 f. Sounds too low but could be correct I think. My old athlon 1.4 runs at 120 f under load with a volcano 7 on it.