Hi there,
Which version of the AthlonII 250 CPU do you have? Is it the one with C2 or C3 stepping? (If it is the C3 stepping version you will need to update bios to F7G)
If you are sure that you have correct bios for your CPU......... re-set everything in bios to optimised defaults. (I know this seems like going backwards but it is better to start with everything returned to their default settings). Reboot and check that your system is OK
Once you have done that, can you re-post with some further details as to how the system is (without tweaking), and what you are trying to achieve. It will then be easier to point you in the right direction.
Cheers