Visual Studio 2015 can't read settings from csproj file

Yesterday my VS2015 suddenly stopped being able to read the settings from any csproj files, and I've no idea why. There are several symptoms of this:

• I get many warnings when opening a project, saying "Load of property 'OutputPath' failed", "Load of property 'AssemblyName' failed" etc. etc.

• Most tabs on the project properties page are blank and read only

• The Resources tab on the project properties page often gives the error "Error loading type library/dll. (Exception from HRESULT: 0x80029C4A (TYPE_E_CANTLOADLIBRARY))"

• An error occurs if I try to open the designer for any forms ("The designer could not be shown for this file because none of the classes within it can be designed....The base class 'System.Windows.Forms.Form' could not be loaded....")
• I can build the project but the exe does not appear in the bin\Debug folder (the vshost.exe does appear), and if I try to debug then an error dialog pops up saying it couldn't find the exe and then "...Please build the project and retry, or set the OutputPath and AssemblyName properties..."

I don't know what caused this to suddenly start happening, I have been using VS2015 without issues for a long time. I have uninstalled and reinstalled VS2015 but it made no difference, I've spent a long time searching the web but haven't found anybody else reporting the same symptoms. I'm hoping I don't need to re-image my machine, so any ideas would be gratefully received.

Thanks