AK77-600GN Stability problem

The problem is:
The board won't run stable if the speed settings are correct. If i set the clock on 100Mzh in stead of 166 (Then the Ahtlon2800 appears to be an Athlon 2100 and RAM runs at 266MHz insteadof 400) it runs OK. Addition of a system fan, change of harddrive or memory did not work. It might be a problem with the sATA since the HDD led will keep on burning.