We have recently lost the hot water pressure for our kitchen sink, and in turn have lost the pressure needed to run our dishwasher. We own an old home that is about 80 years old. The hot water heater seems to be in fine shape, though. The washing machine, which is in the basement with the hot water heater, has great hot water pressure. Also, our only bathroom, which is on the second floor, has never had great hot water pressure, but it hasn't diminished like it has for the kitchen. The pipes in the basement seem to be newer and made of copper. However, once they turn and go up through the basement ceiling, they look to be much older. There looks to be only one system of pipes that leads up from the basement, and the bathroom is directly above the kitchen sink.
Also, we have experienced a "bumping" sound coming from the kitchen sink, as if air has been introduced into the line. We do have a sprayer and am not sure if that is the source of the air.

My questions are these:
1) What and where might the problem be?
2) Does this sound like a simple repair that my husband and I (we of very little plumbing experience) might be able to handle, or should we hire a professional?
3) Could the air in the line and the loss of hot water be related?

Thank you.