Since you have 3 hard drives, I'm going to assume that all three drives don't have Operating systems that get booted from. Only one drive, maybe a second. In any case, any partitions/drives that have only data on them (i.e. music files, movies, etc.) you can plug into the new and access without trouble. As for any operating systems, the safest action is to back up the data, and re-install the operating systems with the new motherboard installed.