It has likely been deleted if a search does not turn up the file. If it isn't in the recycle bin, try some recovery software. You are more likely to be able to recover it if the loss was recent, and the drive has not been in heavy use. Otherwise, it may be overwritten already.
If you don't already have recovery software, or something like a protected recycle bin (a la Norton), try these:
http://www.piriform.com/recuva
http://www.undeleteunerase.com/
or search
http://www.google.com/search?ie=UTF-8&oe=utf-8&q=recover+files
Check also to see that the file has not been renamed or saved under a different name. A backup file may exist with a different extension.