I have 4.7GB DVD with me. I looked at it, it has no data on it (looks clean).
I put it into the drive. I hovered over it with mouse and it says "Free space: 0 bytes", okay...
I tried to choose .iso file I wanted to install on DVD. Program is Brasero, which tells me that this disk has only 1.5GB of space left.

And I don't know what's happening, the disk appears to be empty, both by it's content and by the look on the silver-side-thing.

Can someone tell me what's going on?

Perhaps it has data in a format that Windows cannot read?

...it was on Linux... I'm using Windows only when I have no other choice.

Linux Ubuntu 14.04 LTS with Brasero.