I lost the password in a hard drive crash.
First, I'll answer directly. If an American judge believed he/she had the authority to compel you to hand over the data, and you gave the *unable* excuse, the judge would simply assume you are able and rule against you until you found the ability. This may mean you stay in jail, you continue to be tortured, your girlfriend continues to be raped, your kid remains in foster custody, the state takes your money, or whatever.
This has already been thought of. And one answer is engineering some form of plausible deniable.
One idea is to make the existence of encrypted data invisible. Then you could try to claim everything is already visible. But that may not work with a dedicated inquisitor.
In a better designed system, you should be able to provide a password to your inquisitor (the government, perhaps) and it would appear to be successful. But in reality, yet another password would be needed to get at the hidden data.