DVD Drive Reading cds only

My DVD drive is not reading any DVD. I tried to open my computer and clicked on the CD/drive icon and it says please insert any disk into the drive.
Whenever I put the CD into my drive it plays well but whenever I try to play a DVD just light blinks for some time but nothing happens.
I bought a new DVD drive which works well with only CDs I have purchased, but it doesn't recognize CD/DVDs written by me or someone else, I think it is a software problem but does anyone have any advice what can i do or where to start, thanks.
I am using Nero Express to burn a CD in Windows Vista.
Is there anything of which i can repair my old DVD drive by opening it or by upgrading its firmware?
