When you try to View Source, nothing happens, and you may not receive an error message.
The most common cause is an invalid path for the TMP environment variable.
Use Control Panel / System / Environment / User Variables to select (or add) the TMP variable and type a valid path to your TEMP folder. Click OK.
NOTE: When you View Source, the file is copied from Temporarity Internet Files to the folder specified in the TMP environment variable and opened in NOTEPAD.