Waveform not visible

Why is it that sometimes my waveform is visible and sometimes not - even after I have made waveform larger because I need to see it to edit sound.

Please post a screen shot of what you're talking about and where.

I cannot see the sound wave or picture anymore on my time line... But I think it's because it is rendering...?

It looks like the thumbnails and peak data have never been built. How quickly this happens depends on your system capabilities. Nothing to do with rendering. Quit the application. Relaunch it and wait. Don't do anything until they build. As soon as you start to do something the process will be interrupted.