It has less to do with a problem with your Mac, but, as mentioned much earlier, you need an authoring program to encode your videos/files - aside from being able to create cool customized menus and transitions, iDVD does the encoding as well. It is only available as part of the retail iLife 09 and iLife 11 DVDs and has been discontinued some time ago; however, you can still find them at online resellers and ebay. Neither iPhoto nor the new iMovie version does encoding to be able to burn a DVD playable in a DVD player - they are "cloud" centric - you can share online, but you can't burn it easily. Please note that iDVD is no longer 100% stable in Yosemite (it works well in Mavericks).