fail over

In a computer system, to switch automatically to a spare, backup, or alternative component when another one fails. We've put new protocols in place to ensure that the computer will fail over to functioning memory blocks in the event of a critical error. The system cannot be down for this long a period of time. Why didn't it fail over to the backup? Can we configure my computer to fail over to another power supply in times like this? I'm sick of losing work all the time.