Sounds like this leak has been going on for some time. The water has probably soaked through the hardwood at the joints and has gotten into the subfloor (usually plywood or OSB) and has loosened the glue in the sub floor material. To properly repair will require removal of the hardwood (you may be able to salvage if you do it carefully - number each piece so you can put them back where they came from)and replacing the damaged sub floor. Then, reinstall the hardwood and refinish it as needed. If this sounds like more than you can handle, contact a local home repair company and get an estimate (probably should get at least 3 estimates and check the BBB, etc.) Hope this helps!