When I click on File >Open >PC nothing comes up and the program crashes. This was on my older version and have subsequently tried it on the latest 64-bit and 32-bit versions with the same result. Can anyone suggest a fix please? Thanks in advance.
You have to be careful having 64-bit and 32-bit versions of Audacity on the same computer:
you have to keep them separate otherwise corruption will ensue
I removed one before trying the other. 
Did you remove the hidden Audacity folder ? …
Users<username>\AppData\Roaming\audacity\
That where the corruption happens.