Pixellated video is most often caused by dirty heads on the camcorder.
Pixellated video is shown by squares of video are misrepresented on the screen, so you may get black squares, squares containing information from a recording underneath if you are reusing the tape, squares containing information from what you recorded a few seconds ago or information from adjacent pixels. Dirty heads can also lead to audio problems, such as distorted sound.
What we do about this depends on what point the pixellation occurred, which can be at the point of recording or the point of playback.
If the heads were dirty at the point of recording, then the pixellation will have been recorded direct to the tape and unfortunately you will not be able to recover the full video, as it just wasn't recorded. Dirty heads at point of recording will always have the pixellation at exactly the same place.
If the heads were clean when recording, but have since got dirty, so when you play back the movie the heads cannot read the information properly then cleaning the tape heads will recover the movie, so long as we haven't played the tape too many times on the dirty heads and transferred the dirt to the tape itself. Pixellation on playback from a clean recording will show up at different points each time the video is played.
The first thing to do is to clean the tape heads using a proprietary tape head cleaner. These are slightly abrasive, so should be used STRICTLY in accordance with the instructions supplied.
After cleaning, check the tape again and see if it now plays properly. If not, another clean may solve the problem.