Try this - go into the BIOS screen on reboot, and press ctrl-F1 . This will unlock a hidden menu called Advanced Chipset Options. In there you can change your DDR2 timing and speed, your HT multiplier, and a couple other things. Set the RAM to manual and 800, leave timing alone for now. That should fix you up. Also, check the voltages on the RAM. If it is 2.1V ram you will need to up the RAM voltage manually, the mobo only puts it at 1.8V, which will usually work, but only under JEDEC specification which are usually lower freq, lower timings, or both compared to 2.1v on RAM designed to run at 2.0 or 2.1v. If your RAM is higher voltage than 1.8, you will need to go under the Intelligent Tweaker section and set the DDR voltage to be higher. If it is 2.1v RAM, set the voltage to +0.3v in the BIOS, 0.2 if 2.0v, and so on. That will sometimes allow it to automatically run at EPP rated speeds. It will be in red and warn you about overvolting, but in this case you can ignore it IF your RAM is designed to run at 2.1v; all you are doing is giving it the correct amount of power.
Give it a look, hope this sorts you out.
