creaking floors drive me & my customers mad!
1. Is this traditional floor boards?
2. Chipboard flooring
if old timber consider checking whats under the area thats creaking- for example
heating pipes can cause the floor/joists to twist etc
Replacing nails with screws is great - but check what underneath!!!!!
it could have live cables, or heating or water pipes.
sometimes additional support timbers are needed (noggins)
take your time & ensure you know whats under the floor before doing anything