i have since found if i turn off hyper threading ( p4 3ghz ) it doesn't turn black ( was doing it at various times during conversion ) but either way it doesn't seem to make any speed difference in fact with hyperthreading on it takes about 2 min less to do the same conversion..
being new to winavi previously used nerovision 3 and vso divx to dvd i am at a loss to find out what is happening when the progress bar turns black is it a lack of memory???