CD controller yellow mark

Under Windows 2000 my Plug and Play CD and CD-RW worked fine. I do not know what I did, but now they are recognized and installed, but with yellow exclamation mark. I did uninstall and reboot with autodetect several times. I cannot access them and they are not shown in explorer. Troubleshooting says Error code 19, a possible registry problem.
I am lost, can anyone help?