Try to change the extension of your tiff file to other major image formats and open them in a photo editor. If you have a Mac, download and install GraphicConverter and try the previous solution until the software recognizes one of the formats. Changing the extension of your file from .tiff to .tif or the filename might do the trick also. If none of the solutions works, try the following suggestions. Update your Photoshop application to its latest version. To do so, open the software, go to Help, Updates in Photosop CS5 and apply all of the updates listed under Adobe Photoshop CS5 in the Adobe Application Manager. Restart your system and try opening the file. Else, try a photo recovery program, such as PixRecovery.