It is likely that your project has indeed become corrupted for whatever reason.
Depending on what’s in it you should “Export Selected Tracks” or “Export Midi”, and then import those into a new, empty file. (There is no Import Selected tracks, instead it’s called Import Track Archive)
(A Track Archive contains most Cubase data that goes with the track in addition to the MIDI or audio itself see page 696 of the operation manual)