nero fails to burn dvd-data disc

hi guys, new to this forum.

i use dvd-r disc to burn dvd-data for my movie/anime collection. (cause it stores a lot more if u burn it to data than video.) i'm using nero burning rom(tried to use nero express too). but lately, everytime when i got to about 62%, the 'used buffer level'(at the) top drops from 100%, so does the buffer level, to like 10% and then it raised back up to 100%. but, the 'buffer level'(at the bottom) stayed at 32%(if i picked 4x speed, and 11% if i used 8x speed) it was 97%-99% when it's working. i tried to give it time(about a day) to let it raise back up, but it's not working. it just stays there. not that it's frozen or anything. so i have to cancel it.

please help me guys, i just don't know what's the problem. and i've already wasteed 4 dvd-r discs. or maybe a should switch it to another program?? or is it my burner's problem? oh and i'm using SONY DVD RW DW-D22A writer.

i know it's confusing but any help would be greatly apreciated
thanks in advance

hakuron