One could also say an encrypted hard drive is like the GPS location of a coffin containing a dead body. Can the authorities compel you to reveal the GPS coordinates of the body? If you deny any knowledge or reveal that you "forgot" the coordinates, could you be compelled to provide access to the evidence? What about GPS coordinates to a stash of drugs? At what point does revealing incriminating information become protected by the 5th amendment?

Do you need to provide a key for a locked filing cabinet to the authorities though? They are free to break the lock with a proper warrant.

You don't need to provide the key, just access to the contents. Or they can break the lock. But an encrypted drive is like an unbreakable lock.

If you had an uncrackable safe could they compel you to open it though?

Yes. They can't compel you to give them the means to open it (e.g. tell them the combination), but you can be forced to open it for them.

Then if you are guilty say of murder, the best strategy is to refuse. In that case, you'd be only liable for contempt of court.

That depends on whether they can hold you indefinitely for contempt of court. It has been my understanding that in some jurisdictions, they can.