What you did is correct something is wrong with your preview app. Preview is use to open jpeg files and others, so maybe when you are trying to open a file with preview the file may be corrupted thus damaging the preview app.
1) Do a virus scan. Try using iantivirus download from the internet and do a full scan ( Iantivirus have many types, use the free version and do a full scan.)
2) Second, instead of clicking preview, try to right click it. You will see two options, click on open and see whether it works.
3) Go to any jpeg file and try opening them with preview again. This time when you go to the file, right click them. Click on open with and select preview.
You can also use preview to open any other pdf files, try opening pdf files then.