Manager missing frame

After a server move and then an upgrade to 2.3 I now have a manager and dashboard page, but although the tree appears on the left there is nothing appearing on the right.
So, can't edit any pages, packages, users, system settings etc etc

So far have tried
clearing cache, automatically and manually
re uploading all manager files
re installing 2.3
checking config paths are correct

Also get error from MIGx, but as can't get into packages I can't disable I install anything.
IndexManagerController not found.
Some extras do appear normally, Version X and Batcher

As usual, site about to go live and just thought I had better upgrade before launch, and now stuck!

Any suggestions?

The first thing to try is clearing your browser cache *and* cookies and turning off the compress_js and compress_css System Settings (in the modx_system_settings table in the db if necessary), then deleting all files in the core/cache directory.

If the right part of the manager doesn't show up, it's often a javascript error. If you open the browser dev tools, do you see any 404s or errors in the console?