View Source does not work in Internet Explorer (IE)
This is a problem that I ran into on several computers when working on web projects.
On some PCs the menu item Source in menu View seems not to work as if the web page's author would prohibit it. The same web page will surrender its source easily if viewed with Opera, I found.
Because of heavy surfing habits ;-) the web browser's temporary file space had been completely used up. The solution is to either allocated more space for temporary files in IE or to delete the existing temporary files.
Go to menu Tools | Options, stay on tab General and in the middle of the screen, click on button Delete Files.... Alternatively you can click on Settings next to it and allocated more space, thus having the problem occur again a bit later.
A little nuisance.. if you do either of these 2 steps and then try to view the pages's source, it will still not work. You have to reload the page - then it will work. Apparently IE does look at how much disk space is available only once when the page is loaded, not in the moment when you request the source code. (as tested with Internet Explorer version 6.0)
Had I known this 2 years ago, it would've saved me a few Opera installations and gray hair.
Alternatively you may also go to the start menu and type: CLEANMGR.EXE and hit enter.
This will start Windows' disk cleanup utility - it will suggest to your Temporary Internet Files.