Reading Dvd



I have an Ibook G4 that is only about a couple of months old. I was able to install the OS in it using the DVD drive that came with it. but when I put in one of the DVD in which I had some data stored, it simply will not read it. Some time it even does not eject the DVD if I keep the F12 key pressed. I had to restart the machine to get the DVD out.

I am able to read CD and also other movie DVD, the DVD that contains the OS X etc.

I can read the disk, that I am unable to mount in my iBook, on other machines. for example it works okay on the power book my friend has.

the problem is not with only on DVD, there is a whole set of DVDs
(similar type Moserbaer pro, DVD-Recordable) that I am not able to read.

Can anyone tell me what the trouble could be?