some boards used to have a little tempreture sensor in the middle of the cup socket... so they wernt very accurate, were slow to show the real temp as the cpu warmed up... and some even had a draught blowing over them from the HS fan !
tho youre on an amd64... so it should deffo be using the internal temp sensor thing built into the cpu....
if you leave it running in the bios for 30min it should reach its max temp, as the biso leaves the cpu going at 100%.... try that and see what happens
tho Id say its not an overheating problem... if hitting reset just after you start up fixes it for a while...
what does the beeping sound like ?
could it be the gfx card overheating ?