It's a Rockhopper, not Hardrock, you can see that by looking at the top tube.

For the year, thinking it's around 2000/1, you can research Bikepedia for the exact year 2000 Specialized Rockhopper A1 FS - BikePedia

For the crank, you need to ID what you currently have, from the age, it could be Square Taper, ISIS or Octalink, for length, if what you currently have works, choose that length, it should be printed/stamped on the back of the crank, probably near the pedal hole