Two things about CompUSA I learned the hard way:
1. Save all of your paperwork and know exactly where it is. If you ever need to use their maintenance agreements, you have to present the paper, or they will not honor it, at all. They have absolutely nothing on computer to "look it up".
2. If they ask what happened, tell them you don't know. Period.

I bought an iBook about five years ago, with a 3-year plan. The keyboard got a few drops of water dripped on it, and made the X and Z keys not work. I scrambled for the documents, and couldn't find them. I had to hassle them for a month to honor it with no paperwork, before they did. Then they asked me what happened, and I told them. I told the truth, and they said, "That is abuse - We don't cover abuse." If I would have simply said, "I dunno", they would have covered it.

Just say: "Who knows what went wrong?". That's not a lie -- it is merely a rhetorical question.