Nero Visual Problems

Hi everyone

Could someone please help me sort this problem out? I am running windows xp and have Nero version 6 on computer. I have downloaded avi’s from internet and have not had any problems burning these before. Now i can not preview any avi before i burn them and all dvd that i used before are no longer valid disk to burn on so the message says at the end of burning. I have tried dvd-rw, dvd-r which is recommend for my burner and they are no longer compatiable. I have a LG GSA 4163B dual layer burner and this problem has only just started. I forgot to mention i have audio but no picture when i preview these avi’s.