Cubase 9 Pro Video Keeps Disappearing

I’m working with a video in 9 Pro and am having problems. The video (Mpeg-4 H264 AAC audio) imported fine and played OK for a few days. But then this week when I re-open the project I can only see a black screen in the video player. I can hear the audio from it and see thumbnails but nothing in the player.

I opening the file in Quicktime and it worked fine but then when I have tried to re-import it now says ‘invalid file format’ for the video. What’s hapenned??? I haven’t run any updates or anything. Nothing changed since last week. I know 9 doesn’t use Quicktime any more as a player but why would it suddenly not like this video?

An update of sorts: I realised I was using Pro 9.0.00 so updated to 9.0.40 and it now imports can view the video. But when I try to play a section or record the video starts to stutter and Cubase freezes up for about 10 secs before I get an error message in Windows saying

“Display driver NVIDIA Windows Kernel Mode Driver stopped responding and has successfully recovered.”

After that it plays OK but my cursor has disappeared. The only way to get it back is to restart Cubase.

Any ideas peeps??