Guy locked-up forever for forgetting his password.

[TheRealJoeFish]

See my comment above; I think this is a misinterpretation of the fifth amendment. An officer can force you to let them in your house if they have a warrant. So too can the officer force you to let them into your computer if they have a warrant. This is like saying "having to hand an officer a key to your storage space is self-incrimination for fifth amendment purposes." (Edited to add: if it's not clear, such an argument is specious) The password (like the key) isn't what's incriminating; it's whatever physical stuff is in the computer (storage space).

The fifth amendment is wayyyyy less expansive than most people think. TV has something to do with that.

Let's say that the guy is telling the truth, if only for a hypothetical scenario; in this case, he does not know the password.  How could he possibly give the cops something that he does not have access to?

That's a totally different question. If he doesn't know the password (if he's lost the key), then there's no way he can give it to them.  But that has nothing to do with the 5th amendment.  No, holding him indefinitely for forgetting a password is, rather, an entirely different sort of unconstitutional.