We have a squeeky board under the carpet on a second floor room. Should we use a screw or a nail to try and resecure it? Any pointers on how to isolate the spot to work on, since it seems to cover a few feet as you walk across it.

I would not use screws they tend to get caught in the carpet going in. I would use a small ring shank nail and nail it in then try to counter sink it so the head does not force itself back through the carpet.

Ask This Old House just had a show on this! It was done without pulling up the carpet but he knew the size boards and used a device something like a stud finder to find the cross boards so he could mark the spots where they crossed so to be sure he was screwing the loose board into the support board. Man I am not explaining this well because this is NOT my forte, its my husband who is into this stuff and I was only peripherally watching it as I made us breakfast!

He used special fasteners too that allowed it to go deep enough to catch the joists (is that what its called? I mean go through the top board and sink into the bottom one, I know you guys must be laughing at this LOL) and still be sticking above the carpet. Then a special cutter was used that cut the top of the fastener off flush and the carpet hide it completely. He suggested several fasteners in both directions of a squeak, else the slight warp of a board may overpower just one.

Can you tell a totally non-mechanical type posted this? Gawd. You ought to see what happens when my husband asks me to go into the workshop and fetch a tool. I hope this helped, if only a little?? LOL

we have a squeeky board under the carpet on a second floor room. Should we use a screw or a nail to try and resecure it? Any pointers on how to isolate the spot to work on, since it seems to cover a few feet as you walk across it.
Floor joists are usually 16" on center,use a 12,14,03 16 penny finishing nail (no Head)to locate the joist then pound a finishing nail all the was in.Pull the carpet over the finishing nail.Do this in the area of the squeek and you should eliminate it.