I recently got a new mobo, Gigabyte MA78G-DS3H, and my cpu temps have been going wild.
In bios, it idles at about 52C, and whilst under load playing Call of Duty 4, It hits the 70 mark. I've set in my bios to send a CPU temperature threshold warning beep whenever it hits 70 degrees, and then I check the EasyTune5 Pro (A program associated with Gigabyte mobos) and it shows 71C. I've also touched the heatsink after I shut it down, and it was super hot, barely keeping my finger on it without getting burnt.
I recently find out it might be the voltage, which for my AMD 6000+, 125W, 90nm version, is meant to be set 1.35-1.40. It was set to default 1.40 in bios, so I switched it back to 1.35, but I still get overheating problems. I also noticed that in the bios, it shows the voltages a bit higher (1.42). I've set it lower to about 1.25 where it finally shows the voltages at 1.33, which then I get BSODs.
My case is fairly ventilated with one low front 12cm fan, and a high top 12cm fan, with the PSU having dual fan, intake from case and exhaust out the back. All cables are tied out of the way of fans, and all fans are working. On the side door, it has two, kind of 'open-mesh' things. with the top being a slot for an 8cm fan.
I have reapplied Artic Silver 5 evenly several times, and readjusted the stock heatsink several times as well.
Just to make it clearer: I use an AMD Athlon 6000+ X2 (125W, 90nm)
Case ventilation is an issue - only 2 real case fans. You could also replace the stock cooler with a good aftermarket one, not that stock is terribly weak.
The Athlon64 x2 6000+ Windsor is a hot chip, the highest clocked bin AMD could release on 90nm. Don't expect it to load at <50C without specific attention to the cooling environment; treat it like an FX or EE.