How to Troubleshoot Plugin/Theme conflict if "Network Admin" is not shown in menu?

Hi,

My WP Multiisite install does not show the "Network Admin" link.

I was advised that this could be due to a conflict. Normally to troubleshoot plugin/theme conflicts you would switch them off etc.

However, I can not access Plugins or Themes as I can not access the Network Admin link in the menu or the Network Dashboard.

How do I deal with this?