Just how old, you ask? Old enough to have a dead keyboard that plugged in with a round connector. And... a replacement keyboard that had a USB connector. The desktop tower, though newer than the keyboard, still boasted round keyboard and mouse connector ports, in addition to sporting several USB slots.
Doesn't sound confusing, does it? But a client recently was given a replacement keyboard and was confounded about how to connect it, because they had never, ever had a keyboard that didn't have a round connector. So they brought it back to the store and asked for a keyboard they were more familiar with. Suffice it to say, round connector keyboards haven't been made in many years. A testament to their longevity: my client had the old keyboard for more than 15 years.
The client brought the USB keyboard back home, plugged it into an empty USB slot, and you can guess the rest of the story. The quick brown fox jumped over the lazy dog. All the keys worked!
ALWAYS REMEMBER: before calling for help - is it plugged in, and is it turned on?