Sound stopped suddenly
It is actually a hardware issue. I am attaching the link that helped me to narrow down to the problem. https://web.archive.org/web/20121226203752/http://en.community.dell.com/support-forums/laptop/f/3517/p/19352413/19772968.aspx
Copy-pasted from the link:
Use this FAQ when you have no audio from both the speakers and the headphone jack. If you have no audio from the speakers but do have audio through the jack, see the Headphone Jack FAQ.
If you just re-installed your operating system and do not have audio, go directly to Section 7 of the Audio Driver FAQ.
I. General Steps
Perform these general steps in any order.
Configuration Settings
Make sure the volume is not turned down or the speakers muted. Open the Sound properties and check each setting for proper configuration. In addition, each audio application or player you use will have its own settings. Use a common audio file player when testing audio, such as Windows Media Player instead of itunes for example, and play files from the hard drive, not off the internet. The idea is to keep it as simple as possible in order to reduce potential configuration issues and problems with the applications themselves.
Check the default audio device setting and make sure it is set to your device (Sigmatel, IDT or Realtek) and not usb audio, HDMI, etc..
[...]
Re-install the Audio Driver
Do a simple reinstall. Open the Device Manager and find the audio driver under Sound Controllers (it will be named Sigmatel, IDT, Realtec, or Crystal). Right click on it then click "uninstall" and do not select the option to delete the files. Restart the computer and Windows will reinstall the driver. The reason this process fixes some "no audio" problems is because it resets the driver configuration to its default settings.
Install fresh driver files. Go to the Dell driver folder on the hard drive. The location is c:\dell\drivers
Expand all folders and all subfolders there. Delete all folders that have a subfolder named "WDM". Those will be the audio driver folders and it is safe to delete them.Next download a new audio driver package from your computer's driver downloads page. Go to the Driver & Downloads Home Page and follow the links to select your laptop model and its operating system. Expand the 'Audio' category and download the audio driver named Sigmatel, IDT, or Realtec. Do not download anything named "Creative Labs" at this time. Next, unzip the files and install the driver. When you unzip the files they will be unpacked by default to a new folder on the hard drive at c:\dell\drivers\Rxxxxxx -- similar to the one(s) you deleted except that it will have fresh files and it will be the newest version of the driver if you did not already have that.
II. Hardware Diagnostics
If the general steps did not help, do a diagnostic analysis of the computer to discover the problem area which is the cause of the symptom. Diagnosing "no audio" is a process of eliminating potential problem areas and eventually narrowing down to one problem area. These hardware tests can narrow the problem down to either the software or hardware. This is important to know because if the hardware is shot then no number of software solutions will fix the problem and will just just be a waste of time. When doing the tests do not use usb headphones or usb speakers.
Sense Pin Test. Connect headphones or external speakers to the output jack and listen for audio. The reason for this test is that if audio comes through the jack but not through the internal speakers, that is one of the symptoms of a failed sense pin in the jack which is a hardware problem that the audio tests in Dell Diagnostics will fail to detect, so you have to test for it specifically. If this test does produce audio from the jack but not the speakers then see the Headphone Jack FAQ to find out how to complete the diagnostic. Note however that the failed sense pin problem will only occur on Dell laptops with HD audio (all models built in the last 6 or 7 years), not the older models with the AC97 hardware codec.
Dell Diagnostics Audio Tests. These tests are designed to narrow the problem area down to either the hardware or software, and will detect the existence of any hardware failure except the failed sense pin mentioned above. If the computer cannot pass these tests then there is no need to attempt any software solutions. Do not confuse these tests with the PSA tests which will run first but will not definitively test the audio hardware. See the Dell Diagnostics Audio Tests FAQ for more details and instructions.
Original Factory Configuration. If the Dell Diagnostics audio tests cannot be run then an alternate test is to return the computer to its original factory configuration. This is usually done as a last resort solution, but it is also a diagnostic tool because if it does restore audio functioning then the problem area is the software, and if it does not restore audio functioning then the problem area is the hardware. To return the computer to its original factory configuration for diagnostic purposes, use PC Restore for XP, or Factory Image Restore for Vista and 7. The instructions are in the Owner's Manuals and Setup Guides.
Note that there are 2 problems that this will not correct: the bad sense pin mentioned above, or a problem with bad firmware on an optical drive or other device, because the firmware is stored on the device itself. The system BIOS is also firmware. However bad firmware on a device will not cause the "no audio" problem that is the subject of this faq.
III. Software Problems
If the laptop passes the hardware tests then logically the problem area is the software (except in the case of a bad sense pin).
- Audio Driver
Often the driver is the cause of the audio problem. Re-install the driver as explained above. [...]
IV. Addenda
Some additional things to look at particularly on older models.
Other Hardware Problems
Headphone Jack. As explained above, a jack can have a failure of the sense pin. However that is not the only possible jack problem -- particularly on older models that do not have a sense pin. See the Headphone Jack FAQ for more details and a list of the models that have replaceable jack circuit boards.
Modem. In some models the modem can have a problem that interferes with the the audio system. Symptoms include inability to get the audio driver to install, getting an error message saying no audio hardware present, and audio properties settings being grayed out. To test this you have to physically remove the modem, not just uninstall the driver. With the modem removed, try again to install the audio driver. If the audio works after removing the modem then you might need to replace it. This issue is more likely to occur on older models.
Loose or Broken Speaker Wires. A connection to the speakers can be loose, or on some models the connection to the palm rest which houses the speakers can become loose and cause the speakers to stop working but still allowing the headphone jack to work. Wires are more likely to come loose than to break, but in a few models like the Inspiron 700m & 710m where the wires are routed through the hinges, the wires can pinch during the opening & closing of the display screen and break. Often you can hear some audio through the speakers when the screen is partially closed as the frayed wire ends make contact. For more information on this problem see the Speaker Wires Break in 700m & 710m FAQ.
Speakers. The speakers themselves can stop working. This is somewhat rare but not unheard of. If you hear the test tones when you run the PSA tests then the speakers work. See the Dell Diagnostics Audio Tests FAQ for more about the PSA tests.