Can I assume that your audio is still working? Let's look at a couple of things within your notebook.
1. Open Control Panel than open Sound and Audio Devices.
Click the Audio tab. What should be listed in both playback & recording is device AC97? Click the Voice tab. Same device should be there. Close all opened windows except Comtrol Panel. Open System.
2. Click the Hadrware tab, than click Device Manager.
Scroll down to Sound, video and game controller. Click the + sign to list all devices. Do you see the AC97? Is there any yellow ! points?
3.If you saw the AC97 in all places described & you have no yellow ! point the odds are your internal mic chip is defective.
The only way to fix this is through Dell & they would replace your mainbord in the notebook. However if you wish too I can explain how to uninstall your sound device driver & reinstall the sound/mic driver software just to make sure. Ready?
While still in Device Manager. Right click once on AC97. A small window will display, left click uninstall. Your notebook may ask if your sure. Click yes. Close all opened windows. Re-start your notebook. Right click on your desktop & creat a folder, name it AC97.
We need to go to Dell now. Click the link below.
You'll notice the page opends to your Inspiron 710m.
Click the + sign next to Audio. Click on STAC 9750 AC97.
The download page loads. Click the ( Download Now ) button.
You can either Run it now or save it in the AC97 folder you created. Once the download finishes. Close all opened windows.
Last part. Click the start button, than click run. Click Browse & open the AC97 folder click the file R90698.EXE. Click ok.
The driver software will start to install. Once finished re-start your notebook. To test your mic. Open Control Panel, open Sound & audio devices. Click the Voice tab. Click Test Hardware tab. Windows may run it's own little test befor opening the test page.
Now your at Microphone Test page. Follow the instructions.
If you heard yourself through the testing your mic is working.
If the testing failed..... Than we are back to a defective mic.
I hope this has helped.
If you have any more questions feel free to post them here.
Good Luck & kind Regards