Cause: This may well be caused by a fault on one of the input/output devices attached to the PC, mouse, keyboard, hard drives or removable drives such as CD or floppy etc.  The computer runs a check on all of the devices connected to it before running the operating system, if there is a fault on one of these components it can result in the system going into the BIOS or CMOS.

Solution: First pinpoint the faulting component; whilst in the BIOS CMOS settings - check that the hard drive, CD/DVD and floppy drives have all been recognised by the system, this is indicated by the model numbers and/or names being shown as shown in the example below.

If there is one there (it doesn't say [None]) then that probably isn't the problem.  If something is not shown that you know should be there then the fault lies with that drive and it either needs replacing or mending.  The layout of BIOS & CMOS differs from PC to PC so the example above may differ from yours as will the model numbers and names.

Provided all of your drives are detected, switch off the PC and unplug the mouse, keyboard, printer etc and then switch the PC on again.  If the fault is being caused by one of the peripherals you have just unplugged the PC will now boot up normally and the operating system will start.

Switch off the PC again and plug in the keyboard then  reboot.  If the PC starts correctly then the keyboard is OK.  If it goes back to the BIOS again then the keyboard needs replacing/repairing.  Repeat this process for each of the devices you unplugged until you find the one that is causing the fault.  The device causing the fault needs to be repaired or replaced.

Hope this has helped.