Double click on the sequence in the project window.
Deleting preview should not do this. Maybe you have done something else. Deleting preview files only requires a new render of the timeline, nothing else.
If you are running out of disk space, get another disk, Look at the post "Storage rules..." I posted some time ago.
First, are you sure that you deleted the Preview files, and not your media files? Can you check in Windows Explorer, that your media files are still where you had them?
Next, if it was the former, and not the latter, this should not happen. Did PrPro give you any sort of message, when you loaded your Project? Something like "where is file xxxx.AVI?"
There are instances where Sequence Timelines do not appear in the Timeline Panel. I'd not think that this would be one of those instances, but... is your Sequence still showing in the Project Panel? What happens if you Dbl-click on it there?
Do start checking the sales for hard drives. Editing video without enough hard drive real estate is asking for problems. It will be money well-spent.
It looks like parrots here.
Thank you!! Thank you!! Thank you!!!
I assume by your remarks that the problem is solved. Happy editing.
BTW: Please indicate the topic as Answered.
I would say "... great minds... ," but that would give me far more credit, than I am due.
I hope that Elio got it sorted out. Kinda' looks like it. Still, no clue as to why his Timeline would "collapse."