All iPhone 4s pics not showing on Windows 7 PC
Have you enabled iCloud Photo Library? If you have, go to Settings > Apple ID > iCloud > Photos to see whether you tick on "Optimise iPhone Storage". If you've ticked on this item, then that will explain your situation. If you enable this feature, it's normal for you to see just a few photos showing on the picture folder, because the rest of your photos is optimised to thumbnail and won't be shown on computer.
In this case, you should check your iCloud. All photos in your iPhone 4s will be stored there.