I was given a desktop computor where you had to push alt & contol key then delete to gain access; from there you hit enter and the computor would open up. This worked many times until recently I must have hit a wrong key. I've unplugged the computor and all ports twice and have used another keyboard. The problem on the screen announces keyboard failure

Ctl + Alt+ Del is the normal way of starting up a networked computer on say Win2000 or XP etc.
It does sound like the keyboard controller has packed up and as that is part of the mother board, not easilly replaced. Try holding F8 key down as it boots, if the computer goes into a DOS menu, then the Keyboard controller is OK and you have to figure out how to reset the network setting on the PC. but you won't be able to do that without a working keyboard.!
You may have to format the hard drive and put a fresh sytem on it if the keboard driver is missing as there is no way of driving the system without an active keyboard.