[Malcolm]

Further to your problem, download this: http://www.nirsoft.net/utils/shexview.html
Then do this:

1. This program does not require installation, just right click and run as Administrator
2. From the menu, click on Options then click on Filter by Extension Type and select Context Menu
3. On the list, you'll see some of the entries with pink background, those are installed by the third party software
4. Hold down CTRL Key and select all of them then click on the red button on top left corner to disable.
5. Click on the Options again and select Restart Explorer
6. Now try to right click on desktop to see if it fix your problem. If it does then start to enable one by one and repeat step 5 until the problem occurs again, that's the offending extension.