Choppy playback in timeline

Hi

I've had Premiere Elements 18 on my machine for about 3 months and it's been absolutely fine until a couple of days ago.

The problem now is that playback in the time line goes all choppy once I start trimming and deleting parts of the clip. However the clip plays smooth until I start the trimming etc.

I've tried uninstalling and reinstalling PRE but that hasn't made any difference.

A few days ago I installed Lightworks and then uninstalled it again - could this have been the problem?

Does anyone know how to fix this?

Thanks

Jonathan