If it's just the hard drive, it should be fine.
If you do need to phone, the "trick" questions aren't really tricks: you just need to know how many machines you're allowed to install your version of Windows on: usually one. When they ask you how many it's running on, say "one", nothing else. For example, don't witter about "well it's a new hard drive and I'll keep the old one as a backup". They'll refuse to revalidate without telling you why. They're following a script, they have no leeway.