Some CDs not mounting

[Grzegorz Stefanek]

Some CDs, when inserted, just keep on spinning, with the sound they usually 
make when mounting, but nothing happens. All I can do is remove them (with a 
button, eject command has no effect). Those cds work perfectly on my 
girlfriend's laptop with Ubuntu Dapper (I've got Kubuntu).
Can anyone help? It's actually a significant portion of cds, so it's a major 
issue for me.
Thanks in advance.
Grzesiek