Uhmmmm, this is a vexing issue. The FSB bus speed should not affect the speed of the CPU. Check to see what the BIOS tells you about the speed.... How old is the machine? Is it a brand name machine? How dirty is it inside? Based on the info you have provided, perhaps re-seating the processor might help (clean it good), and if the fans are on their way out, perhaps since the RPMs can not go full speed on boot then the processor is slowed to make allowances -perhaps replacing the fan?