Hi, Kathy. I can't tell which of two things are going on from your letter but you should be able to figure it out from checking. It could be that the floor is moving because somebody changed something in the joists under the floor, or the sill are rotting or something like that. In this case, find and fix that problem so the floor and the structure under it is back to level and the boards might come back over time.
The other thing is that someone let water stand on the floor for a long time and the flooring warped on its own. Your option here is to sand it down to level, fill cracks, and refinish.
I know that neither of these options is going to be easy to fix. One other thing occurs and that is that the floor might be one of the "engineered floors". The first thing to do then is to check your paperwork and see what brand it is, how thick, whether it came with a warrantee and whether it is still in force. If the warrantee is still in effect, you can check on having the flooring replaced. If it is no longer under warrantee but you can figure out what brand it is, you can check on replacing it with matching product.
The first 2 options will be difficult and expensive fixes but it is unusual for full 3/4" solid hardwood flooring to buckle without something pretty serious going on. Having problems with an "engineered floor" is a lot more common, cheaper and easier to fix or replace and usually just the result of poor installation.
Sorry that I can't give you any more direction but now you will have to play detective. Good luck. Henry in MI