My computer keeps saying no audio devices found, Please Help!!!

Try using System Restore to get the Registry back to a time before the problem first occurred. In XP, go to

Start>All Programs>Accessories>System Tools>System Restore
and tick 'Restore my computer to an earlier time'. 

In Vista, type 'restore' into the Start menu search box, and System Restore will appear in the start menu.

I downloaded the Dell Notebook System Soft ware, the Intel Mobile Chipset Driver, and the Sigma Tel Audio Driver, but when I tried installing all three of them an error popped up saying that the application is missing files.

Did you try to install them all at once? You should do a restart after installing each one. Before installing a Sigmatel again delete any on the hard drive. Go to your hard drive
 c:\Dell\Drivers\R...and delete any folders whose 'R' names correspond to a Sigmatel driver. The Sigmatel folders will be the ones that have a subfolder named "WDM". There could be none, one, or several.

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Try running the audio tests in Dell Diagnostics. These interactive audio tests are designed to narrow down the problem to either the software or hardware. The tests are independent of Windows and drivers, meaning it doesn't matter if those are working correctly or not. To run Dell Diagnostics

1. Restart the computer and tap the f12 key as soon as it starts to boot up .
2. Select 'Diagnostic' from the boot menu. The computer will run its pre-boot assessment tests (PSA) before Dell Diagnostics starts. During the PSA you will hear some tones through the system speaker but this does not adequately test the audio hardware. Dell Diagnostics plays an instrumental piece of music complete with drums, so if you only hear some tones then you have only run the PSA.
3. Dell Diagnostics should open after the PSA tests, or you should see an option to open it. If you have ever reformatted your entire hard drive then Dell Diagnostics will no longer be there as an option. In that case run it from the Drivers and Utilities (Resource) CD if you have one.
4. Select 'Custom', then the audio tests. (At this point - after you have opened Dell Diagnostic custom - if you can't find the option to select the audio tests that is a symptom of a failed audio chip.)
5. The tests will run. Alternate between using headphones and listening to speakers in case only one signal path is working.
The tests will play some audio and ask you whether you heard it.
6. If you don't hear the music during the test it definitely means there is a hardware failure somewhere in the system. In this case Dell will repair the computer if it is still under warranty.
7.If you do hear the audio during the test but not when you boot back into Windows, that almost always means the hardware is okay but there is a problem with the audio driver or with Windows.
8. Error codes: If you answer 'no' to any question that the test asks you, the test generates an error code that can tell a Dell technician that you answered 'no' to that question. The test does not know the exact component that has gone bad. Before answering 'no' to a question, make note of the circumstances at that point so you will know in general what the error code means.