Just got a new DC and boot disk doesnt work... is it a Anti-CDR DC?

There are no ANTI CD-R dreamcasts despite the previous post and if there are they are not in the US/Canada yet so that shouldn't be the problem. Try burning the boot disc using the settings Big Poppa says to in the big poopa help post in order to be sure a boot disc does not work in your Dreamcast. I had the same problem and realized that it was the setting I was using to burn. The nero version also did not work for me.