I'm not sure what you meant by bootable, but i think you should check the iso first, if the iso itself is bootable or not(likely, if it was an OS disk, it should be). There are programs like Nero,Alcohol 120,etc. that can check for this though.
Please forgive the potentially stupid question here OP, but did you tell your PC to boot from the DVD? This is usually done by accessing the boot device menu while your PC is starting up. The specific button to do this will depend on the model of the Mobo, but common buttons are F10, F12 and Delete (NOTE: Not Backspace!).
Yes, I "told" my computer to boot from the dvd in the bios. But I have already figured it out, it turned out that the ISO file was corrupted. So i got a new ISO and it worked.