Did you click Start>All Programs and see if Windows 'Picture Viewer' is present on the list?
If it is not:
You may try using the System File Checker tool (SFC.exe) to troubleshoot missing or corrupted system files.
1. To do this, click Start>All Programs>Accessories, right-click Command Prompt and then click Run as administrator.
2. Type the following command, and then press ENTER: sfc /scannow (note space between sfc and forward slash)
The sfc /scannow command scans all protected system files and replaces incorrect versions with the correct Microsoft versions.
For more information on using the System File Checker tool, you may also view the link below: http://support.microsoft.com/kb/929833
If the issue persists, you may also check if the issue occurs using another user account.
Once restored you will notice that 'Picture Viewer" is very basic and you cannot edit photos with it. If you wish to edit your photos you must install 'Live Photo Gallery' which was deliberately left out of Windows 7. Windows Live Photo Gallery 2011
Post back and let us know how you make out.