VCR question?

My Matsui combined television and vcr tapes programmes perfectly but when I playback the video the picture is terrible in all respects. The picture by the way when watching untaped programmes is great.

The problem began when I once played the videos on a separate Nicam vcr. I noticed that as soon as I started playing back on my normal Matsui the picture was snowy, dark, black and white etc. The sound is normal. What could have gone wrong? No good asking me to track channels etc as all tried in vain.