|Assuming the picture files themselves are OK (most likely) and you prefer to use the default viewer:|
Set yourself to show all file extensions. Go to Control Panel > Folder Options > View
Untick "Hide extensions for known file types" (if you are not already set that way).
It is worth keeping that setting.
Now have a look at what the file extension is for one of your pictures - the chances are that it will be "jpg". If so, download this little fix:
When you unpack it and run the exe file, put a tick in jpg (at least). You might want to search for other picture file types shown, to see if any of those have been hit too.
If you want an alternative viewer IrfanView is very good - free and small.
Ms Hulot goes horse riding