|OK, lift up the keyboard and walk away from your computer - if you can get more than 6 feet away from it then the keyboard isn't plugged in ;-)|
But seriously, are the keyboard and mouse wireless or wired? If wireless, have you checked the batteries, if wired how are they connected - USB or PS2? If PS2 are they in the correct sockets - they should be colour-coded. You need to give a bit more information to get a sensible answer.
"I've always been mad, I know I've been mad, like the most of us..." Pink Floyd