By "device mapping table" do you mean the BIOS screen? It's usually a text screen that says AMI or Phoenix with a list of the processor, memory, and devices below. When you say "type exit" do you mean you have to type that word or hit an F key like F2 or F3? If you are in BIOS you might have a dead CMOS battery, the little round one on your motherboard. It is 3 volt so you could remove it and test it with a multi-tester. If it's dead, replace it and re-set your BIOS configuration. If that's not the problem we need more information about the "device mapping table" screen you are describing. Thanks