Having problems with my blank dvd-r

I'm burning some files with my dvd-r and its going well but on my fourth dvd-r the computer says cannot complete formating why is that? I tried my other blank dvd's and its the same response as if my computer suddenly cannot read the blank dvd's but i"m using the same brand I did not have problems with the other I've successfully burned files on 3dvd-r. what do you think went wrong? pls help me I'm really not that good in computers just the basics you know. I'm using a laptop compaq core2 duo, i hope you can help me guys thanks so much.