Solid Hardwood, Engineered and Laminate Flooring - Fixing Hardwood Floor Squeaking??!!

I have a 1945'ish house and the whole house is hardwood floor. The upstairs is really bad. There are about 10 different lose boards that squeak and make a terrible noise. How can I fix this?? I have a 14 month old who is a very light sleeper. I woke him up 3 times last night b/c I was walking around up there. Please help.
Thanks so much!!!
Chris

The best way is from underneath, but you have a ceiling downstairs. You have a couple of options. Top nail and fill the holes. Screw with a finish screw and fill the hole. Use a big screw and plug. Or you can just live with it.

I done living with it!! LOL I have been meaning to get to this little project but I am almost done w/ my new bathroom. The floors upstairs are shot and are in need of some major sanding, but we plan on putting wall 2 wall carpeting up on the whole second floor minus the bathroom. I hate hardwood floors, even if they are in great shape. Only hardwood floor in my house will be the dining room soon. I just wanna fix the squeaks before we have the carpet installed. Do I try to nail in the tongue and groove?? THANKS

By shot, do you mean they need a complete sand and finish, or is it all broken apart?

I would use finish screws that have a small head, in the face of the boards, into the joists.

That will be fun trying to find out where the joists are?!! LOL They are not falling apart, but they are dull orange/brown in color. Thanks for the info. I will be doing that this weekend.
Chris