I presume that you used the shortcut Shift+E to try to create the waveform and it didn't work. I presume that you have turned on create waveform automatically upon import in the Program Settings.
Close MEP. Go to the folder containing the video clip(s) and delete the H0 and HDP files. Reopen the project in MEP. The two files will be recreated.
If still no waveform then there is some other problem.