Why are waves clipped in Wave Editor?

I've been using the Wave Editor for years, taking music from a cassette recorder and exporting the sound into the Nero Wave Editor to save the music into tracks, etc.
For the first time, all the music waves that have come from the cassette player have no peaks, highs or lows on the Nero wave editor screen. The wave appears as one solid log of sound without the high and low peaks. It doesn't sound right either. Is this called clipping? And why is this happening now all of a sudden? I'm thinking that I changed a setting somewhere by mistake.
I've imported other music (other than music from the cassette player) and I see the peaks, high and lows perfectly, and it sounds good. What's going on with this cassette player imported music all of a sudden?
Please help
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