jpegs and pictures wont open

Hi, A couple of days ago windows stopped me from being able to open jpeg thumbnails. Normally, if I double click a jpeg thumbnail, the picture would display or I could have option of viewing a slide show of multiple images. When I double click now, the cursor will show an hourglass for a second or two and then nothing will happen. Additionally, when I browse folders with jpegs in and I select thumbnail view, no preview thumbnails apear. If anyone could help me out with this I would be very greatful. It is quite a concern for me as I am a photographer. Please help. Thankyou in advance for your time and comments.