If you can access the motherboard, you may be able to remove the battery for a few seconds with the system turned off. That should reset the ram speed in the bios. Or desktop boards have a cmos jumper on the board. You move the jumper over one position keeping 2 out of 3 pins covered, then return to original position after about one minute. The cmos jumper is marked with white id lettering, if your board has it.