I assume that you have just been burning as make a bootable data disc ?
Use Nero Express then you need to select burn Disc Image or Saved Project, its the bottom option on Nero. The ISO should have the boot information in it.
When the add files window opens it defaults to All Nero Compilations and Images as the file types, use the drop down button to open it up and select image files .nrg .iso and .cue
Then add your ISO file and it should burn ok