If you want to open a Photoshop file without Photoshop, you can use a program like Adobe Illustrator or Inkscape. Adobe Illustrator allows you to open PSD files with just a few clicks, and Inkscape is a free program that can open most PSD files.
PRO TIP: If you are having trouble opening a PSD file in Photoshop, it is likely because the file is damaged or corrupt. Try opening the file in another program such as GIMP or Adobe Illustrator to see if it will open.