My hard drive crashed and I had to replace it but now my subscription key doesn't work. What do I need to do to start my F-secure again
Since this is the beta forum I assume you're using beta version.
Just login to beta.f-secure.com, get the installer from there and install. The installer contains the subscription key and automatically uses it.
There is no need to ask support to reset the key any more. If all subscriptions are used the client offers an option to move a license from another computer.
That's excellent news!