That could have several reasons.
For instance, the files you're trying to download appeared with many hosts (20, 30, 50 up to hundreds), which would indicate faked files.
Read here on how to recognize such faked files:
http://www.gnutellaforums.com/showpo...98&postcount=4
For those files you have started to download with some progress, but now they are stuck......well, this could be because of the host(s) having removed the file, renamed it, aren't online (consider that it was a holiday seasons the last couple of weeks) or simply have stopped sharing this said file....
Read here on how to download music:
http://www.gnutellaforums.com/showth...ght=find+music 