make sure you leave the CMOS battery out for about 10 minutes. or you can move the jumpers from 1-2 2-3 for 30 seconds. did you try changing the FSB to whatever the default one is on the 2800
EDIT: also check your mulitpler. i once put my htt to 240 and my multipler down to like 3 and it said 720mhz i was like wtf. i set my htt to 240 and my mutlipeler to 10 and it was only 720 so i went into the bios and i saw that the mutlipler was at 3 and i was like DOh!
AIM/Xfire - pzerofgh