Cubase 5.5.3 no longer working after 6.5 demo

Can anyone please help.
So i installed the 6.5 demo to try it out. Its ok. Can’t see me upgrading yet.
However, version 5.5 no longer opens. It crashes on start up. Its not leaving any messages in the cubase log and i deleted the video dll to see if that helped but nope, still crashing.
I cleared everything in the appdata/roaming/steinberg to see if 6.5 altered prefs.
I uninstalled all recent installs and nothing.

Any idea?
thanx so much if you can help

What’s in the bottom left corner of the splash screen when 5.5.3 crashes?