Hi Paul,

I had this problem, you can usually recover by closing only the preview window in the task manager.

The solution in my case was to completly remove the net frameworks and reinstall both the latest and the 3.5 version that the program needs:

For Windows Vista / 7:

To repair the .NET Frameworks 3.5 and 4 you need as first to use following cleanup tool to remove .NET 4:
http://cid-27e6a35d1a492af7.skydrive.live.com/self.aspx/Blog_Tools/dotnetfx_cleanup_tool.zip
Once done go to Control Panel then choose Programs and Features and then click on Turn Windows features on or off. Clear the check box for Microsoft .NET Framework 3.5.1 and then click on OK. After Windows disables the feature you will need to go back to re-enable Microsoft .NET Framework 3.5.1
This procedure can take some time to deactivate and activate .NET 3.5.1 and once done reinstall .NET 4 after downloading it from following link:
http://www.microsoft.com/en-us/download/details.aspx?id=17718

For Windows 8:

Go to Control Panel > Programs and Features > Turn Windows features on or off
Clear the check box for Microsoft .NET Framework 3.5.1 and then click on OK. Clear also the check box for Microsoft .NET Framework 4.5 and then click on OK.
After Windows disables the feature you will need to go back to re-enable Microsoft .NET Framework 3.5.1 and 4.5 and then click ok.

If this should not help try to use this tool to see if it find any errors:

http://www.microsoft.com/en-us/download/details.aspx?id=30135

Hope this works for you,

Best regards,

Mark.