Where were you able to view it before?
Were you able to see a small version in Windows Explorer? Or did you have "quick view" installed.
Your file association might also have been changed. .jpg files might have been associated with Internet Explorer before. This will allow for pretty quick viewing. It will just have to open an explorer window and only takes a few seconds.
If you installed a graphics program or other programs that can show .jpg files, it is possible they just took over the file association. Most programs prompt you and ask you what files you want to associate with them. Some older programs and some newer ones still just "take over" the association.
If this is the case, and for example, Adobe Photoshop took the association, each time you want to "view" the .jpg, by default it will open Adobe Photoshop. This can take some time depending on the system.
If the file association is not the problem and you used to be able to view .jpg's in Windows Explorer. You might have changed your settings under Folder Options.
For the particular folder in Windows Explorer you need to 1. "View folder as a web page" and 2. "enable thumbnail view". You can set this by folder or for all folders.
CyBOrz