When the music is playing, does the artist and track show up when you open the last.fm software?
You could try opening the last.fm software, going to Help then Diagnostics while a song is playing and seeing if any errors are being reported.
WinAmp might not be editing the tags properly. Try opening them in a different program, like foobar and checking the tags. Foobar has always been perfect for me as far as tags go.