Illustrator PNG Option Missing

Illustrator version CS6
Please bear with me as I'm not particularly tech savvy and I don't really like going on forums but here goes ...
I am trying to save a document as 'PNG' but the option is not coming up, just BMP. I have tried 'export for screens' and 'save for web' but it doesn't do anything.
It is currently running in 'safe mode' and I don't know if that as something to do with the issue. I have a screen grab of the message it shows on start up re some missing plug ins but I don't know how to attach it to this message. I am reluctant to start trying to correct the problem with the missing plug ins in case I make a mistake.
Thank you in advance for any assistance.
