Is your boot priority in your BIOS set to boot CD/DVD first? Or, most motherboards also have a boot menu option very early in the boot phase. If you've done those, you might try another burning software (I use ImgBurn) and burn it at a slower speed. I still think slower burns are more reliable, lol. I guess I'm old school. Also, check the MD5Sum to make sure the ISO you downloaded is valid. Hope this helps.
Tried AsteriskNOW - You'd think Digium would have the superior product, but they went for the stuperior product
Tried TrixBox - They got all corporate and forgot about the rest of us
Tried PIAF - Took a golf club to it
Elastix ??? LOVING IT ???