Will not boot DVD 2nd Time?

This is for an Aspire 4530.
I have set this up to boot first from the DVD drive. But it will not boot the same DVD more than once.

To be accurate: I tried the same DVD several times in a row without success - power-on and off - 5 minutes between power on. Nor will it boot a different DVD that was in the drive earlier. Even unplugging the cord and powering of and on will not work.

It seems that trying the DVD the next day - after unplugging the power cord - DOES work, but again, only the 1st time.
I can't figure out what does this.

 

It looks like the DVD drive is scratching the media. A new recording boots, but there is a loud high-pitched whirring during this process. It doesn't boot on the next try.

 

I fixed this. By sheer fluke, I pushed on the head holding the DVD's laser lens. It suddenly snapped free; it had just been sticky and could not float on the air cushion created by the drive. The drive has been working ever since.

This really does explain why I could only boot once or twice from each new DVD/CD; they were scratched by the 2nd use. What was once an unbroken recording ring, was now dulled in concentric rings. I lost a few important disks, but most I had copies of. Sadly, my Win XP SP3 CD is gone, as my Ultimate Boot Disk for Windows.