It does sound like a file infector at work.
Just to confirm: The desktop is alright? It is only the laptop that has become unbootable?
You could try a rescue disk on the laptop, it is possible it may do the job.
Try
Dr Web or
Avira rescue cd's. The instructions are available on the pages linked above. You would need a clean computer with a cd burner to download and burn them.
I have no experience in actually using these, so can offer no further advice, nor a guess at how effective it will be, but it's worth a try, and if I wanted the photos back it's probably what I'd have a go at. But you may have to be prepared to loose them.
Was the laptop protected at all by any AV when your guests were using it?
I do recommend
AutorunEater to protect a computer from loading malware via an infected USB (flash) drive, it's an application that installs and then detects any malicious autorun process attempting to load. Many good reviews.
The flash drive you used between the laptop and your desktop should be considered as infected. Assuming the desktop appears OK, I would also run at least a quick scan on it with
MBAM, a very effective anti malware scanner and cleaner. There is a free version on the page linked; all it lacks over the paid version is resident protection. Very good for a "second opinion".