Have you arranged for a replacement?
Unfortunately,it's not that uncommon to get a dodgy optical drive,so just try a new one,not ideal, i know.
its not ideal when you've spent £1200 on your system
This is true. There are a lot of components in your PC.
You will be glad to know that you have only had trouble with around £20 worth of the £1200 system.
I understand, it shouldnt happen and it probably wont again, all we can do is get it sorted as soon as possible.
Do try to stop using those dvd's made out of rocks though.