unable to burn DVD's
I am unable to burn DVD's either from FCP X or from the finder Burn option. The internal DVD burner just spits the DVD back out. I am able to view pre-recorded DVD's. I can't burn an .iso file that I have previously burned on this computer. Any help would be greatly appreciated. I am run Yosemite 10.10.5
iMac, iOS 9.0.2