Problem with Dvd-Rom on Inspiron 1520

Hi.

I have Win 7 Sp1 on on Inspiron 1520.

My DVD RW drive had a problem at first, that it could not read from any Dvd while it had no problem with Cd.

When i inserted into it, there was sounds in Dvd drive but with any eror or messages on windows, nothing happened.

But recently, it does not read alos Cds, and when i insert a cd into it, and by right clicking on the drive abnd selecting open,

this message appears :

please insert a disk into Drive H

What should i do ?

thanks.