Try using this free program to search for it:
SearchMyFiles
It's an AWESOME search program.
It's fast.
It's portable by nature, you just unzip it, and run it!
Did I mention it's fast?
It REALLY WORKS.
Before this one, I tried Search Everything, and thought it pretty good. Indeed, that is also a good program, but it must be installed in the registry to do a normal install, and if you do it that way, well, it's as bad or worse than Windows' own indexing service, best I can tell so far.
I like both, but I believe SearchMyFiles is my favorite searching program of all time. Oh, here's the other thing for this program - it'll search ANYWHERE - not just local drives - that's been a big limitation on many of the search apps, in my opinion.
If that doesn't work, there are a couple other things you can try:
1. Open Publisher, see if it's got a reference to the file, and if so, try opening it - won't hurt.
2. Try data recovery software - on the USB drive, and on your C: drive, and your documents/data drive if that's separate.
Restoration is a good free one, also portable in that it just runs without being installed. Another good one is Recuva, but it has to be installed (unless there's a portable version available for it, which I wouldn't be surprised if there is.
All the above apps mentioned are 100% free.
--
"If to err is human, then I must be some kind of human!" -Me