Verbitim DVD's D drive for DVD/CD has vanished

Hi I hope this is the right forum.

I'm trying to burn some photos off my hard drive onto a disc. I have used Tesco DVD-r's and had to make some room as they wouldn't all fit. I used a programme called Ashampoo cd burner, and followed all the instructions.

It burned because I can see a line on the disk. But when I tried to see if it had worked, I got a flashing green light on the tower and a message come up saying 'the directory name is invalid'. What does this mean please?

Also my D drive for DVD/CD has vanished and the disk won't run. Anyone know why this is please?