Faulty conversion from avi to mpeg2

after converting an avi movie to mpeg2 using im too 3gp converter, when previewing before burning all i am getting is the odd coloured square on screen, why is this

can you play dvd’s and other mpeg files on your pc? You may not have a proper mpeg2 codec installed for proper playback.

have played avi from hard drive, but when i converted them to mpeg 2 they will not play on the pc, all i get is the odd coloured squares, have i missed something, same thing happens on the stand alone player

Check out the guides at www.videohelp.com !!

could the conversion be missing something