You can set the standard response to each of your media drives on the computer. I wonder if your computer has somehow "forgotten" waht you want it to usually do. This could have changed if you installed a new device, etc. I have some that don't always pop up the little dialog box like they used to; probably operator error, and this is how I would go in to fix it:

Start -> Accessories -> Windows Explorer-> My Computer -> right over the drive, click on the Properties line. Click the Autoplay tab.

In the drop down menu you can choose the action (did you put in a mixed data disk, or a music CD or a DVD movie?) and then either tell it to prompt you each time (a dialog box pops up and asks if you want to open it with a program or to view the contents in WinExplorer) or tell it to automatically do something, i.e., mixed content, open using WinExplorer, or a music CD, to open in Windows Media Player). Click to apply, or choose to toggle the radio button to always ask each time the device is activated.

Does this help?

SRS