I don't understand how the prosecution can ask for a default judgement without solid compelling evidence of a crime. Without a discovery of the drives contents I'm assuming they had other evidence.
First, part of the reason you don't understand this is because you are under the impression that copyright infringement for personal use is a crime. It is NOT. This is a civil matter, not criminal.
Generally speaking, copyright infringement is only criminal if you are doing it in bulk for profit. Historically, that meant what has been known legally for about 100 years as copyright piracy, which again in general refers to making unauthorized copies of copyrighted works and selling them.
It is today's media industry which has deliberately attempted to confuse you by labeling downloads of copyrighted material for personal use piracy. It is not. Piracy is a legal term referring to PROFITING from unauthorized copying of copyrighted works.
Now, back to the case at hand: being a civil matter, and not criminal, the court need not require probable cause in order to demand that evidence be produced (although it probably can't be seized beforehand. However, because of this, people have been known to destroy evidence after being served notice of a lawsuit. If they do that for the purpose of hiding the evidence, and the plaintiff can show that, it may be ruled spoliation of evidence, and could result in a summary judgment in favor of the plaintiff.
But despite this not being a criminal matter, plaintiff still bears the burden of showing that spoliation happened, via genuine evidence. In this case, plaintiff's claim of spoliation was not backed by evidence; it was a claim without substance. Defendant had a reasonable explanation for the drive's demise, and plaintiff could not show otherwise.
I also don't understand how a drive can be ruled as evidence if nothing is yet discovered on the hard drive.
Remember that this is a civil matter. Standards of evidence are different. If a reasonable person would believe that the drive contained evidence, a judge might ask that it be produced. It very much depends on the circumstances.