Solid Hardwood, Engineered and Laminate Flooring - Repairing floor boards

Hi,

I have a 13 year old 2 storey townhouse. The base of downstairs is concrete while upstairs are I guess standard floor boards ( particle + plywood ?) covered by carpet. Never take carpet out so don't know. I found that maybe after years of use, the floorboards upstairs are really wearing out. One severe board is actually cracking. When I stand on it, I can hear some crack sound and it would sink down a little bit. Some others are like popping out (loosen nails?) from the joist and they bounces when I walk on them. Some of them are not level (bend down on non-supporting points) ... etc. It makes me really worry cause I don't know if it would be very expensive to fix. Do you guys think if I can fix this by myself? I am not very good at home improvement stuff. But I could get access to tools from my friends. Please give me some insight.

The main questions are:

How to take out the carpet and put it back properly after fix?
How to replace broken/cracking floorboards? Completely take it out or take it out only broken areas?
How to fix popping ones? Putting screws in or replace them also?
How to fix bending floorboards? Replace them as well?
Or would there be other problems that I don't know of? I don't think it is water damage since it is in master bedroom.


Thanks

My advice would be to call a pro and get some info first hand. Without being able to see the floor and address these problems first hand any help would be tough.

Philly