Are you using OS X? What sort of Mac are you using? What apps. are you trying to burn from? I don't know about the 4521b, but 4163b works wonderfully in 10.3.x and 10.4. Try downloading and installing Patchburn, it will allow you to burn (from supported drives) using iTunes, iDVD etc. Have you tried using Toast 6.x? Is your drive appearing in the System Profiler? Do blanks or data discs inserted in the drive appear in the finder? What do they look like (option-click -> Get Info) size, type, volume label? Please supply some additional details :bigsmile: and I'll try to help.