When the AT or later CPU chip boots up it transfer into protected mode, then transfers back to real mode (the mode it will use to run DOS). The chip has to reboot to transfer to real mode. Before it reboots, the CPU post a note to itself in CMOS RAM saying "I've just booted. I'm trying to get to real mode to do some work. Don't send me back into protected mode to initialize everything--I've just done that." The likely problem is that CMOS shutdown register on the computer is broken and the CMOS memory and associates chips will have to be replaced; it may be more cost-efficient to replace the motherboard itself.