Try the below mentioned steps and check if this fixes the problem:
1. Check with known good CD/DVD to see if same issue occurs. If no, the issue is with the CD/DVD media not the Optical Drive. Else, follow next steps.
2. Run Optical Drive Troubleshooter from Windows 7 Troubleshooter. MS Fix it : https://support.microsoft.com/en-us/help/2970908/how-to-use-microsoft-easy-fix-solutions 3. Download and Install the Latest Optical Drive Firmware and BIOS from support site. Restart the system.
4. Download and Install Dell provided DVD/BD-playback Software Updates (Cyberlink DVD)