I presume your chip is unlocked if you are trying to run at 9x multiplier. First determine if your memory or
cpu is holding you back i.e. underclock the
cpu to 1.6Ghz (8x200) which it should easily manage at default voltage to see if your memory can run at 200Mhz. If the system is still unstable up the Dimm voltage untill stability is reached.
Now you can increase your
cpu multiplyer to the desired speed and again check for stability. Increase
cpu voltage untill you have achieved this keeping an eye on temp. If you are not overclocking then you shouldn't really have to do this but it won't harm the system.
As far as voltages are concerned I wouldn't go above 2.0 Volts for the
cpu. At which you should get a decent overclock with good cooling
T Addison