You probably need to tell your machine that you want to boot from the DVD. How you do that will be explained in the manual for that machine.
Usually it's just a function key you need to press a few times, but check the manual for what key it is. Failing that, go into your machine's BIOS and set the DVD as the first boot device. If you don't know how to do that either, it's also in the manual.
Mint Testing Team & Mint Donor #3606
KDE 4.11.3, custom preemptive kernel 3.12.2,
Intel i7 4770K @ 4.7GHz, 16GB 2666MHz XMP,
4 Samsung 840 PRO 512GB SSDs in RAID0,
6TB HW RAID10, dual 24" Acer X243H,
Gigabyte nVidia GTX 680 Super Overclock