If your file became corrupted when PowerPoint or your computer crashed, there may be a temporary version of the file in your TEMP directory. If so, you can try the aforementioned Insert, Slides From File and browse to that file. Or you can try changing the file's extension to PPT and see if you can open it from within PowerPoint using File, Open. You could also do a search for *.TMP files on the off chance that it's not in your TEMP directory.
If the presentation seems corrupted or on the verge of it, but you can still open it, download and use the CloneMe add-in from Microsoft (for PowerPoint 97 or 2000) or for PowerPoint 2000 and higher, try HTML "Round-tripping" to repair corruption
Many users have recovered damaged PPT presentations by opening them in Impress, the presentation program included with Sun's Star Office presentation package or the free Open Office.