you can't do a restore if the computer isn't finding it you'll have to follow troubleshooting for not appearing in iTunes first...
1. Ensure the computer meets minimum system requirements.
2. If the screen of the device is blank or displays the recharge icon, charge the device for at least 10 minutes.
3. Check the USB connections. Test with a different device cable and different USB port, if possible.
4. Restart/Reset the device.
5. Restart the computer.
6. Reinstall iTunes and associated software.
7. Check for third-party software conflicts.
8. Use the articles below to try other solutions.
9. Try creating a new user account for the computer to download and install iTunes to and see if the device is recognized in that iTunes.
10. Contact Apple Support for further troubleshooting or to setup a repair:
iPhone technical support: (U.S.)
iPod, Mac and iPad technical support: (U.S.)
Canada technical support: 1-800-263-3394
iTunes: System Requirements
iPhone, iPad, iPod touch: Device not recognized in iTunes for Mac OS X
Mac OS X v10.6 or later: iOS device not recognized in iTunes after restart
iPhone, iPad, iPod touch: Troubleshooting USB connection
iTunes: How to remove and reinstall the Apple Mobile Device Service on Mac OS X
Removing iTunes for Mac OS X
iPad: Turning on/off and resetting
Do you have any other apple devices that you can check to see if they are recognized by iTunes?
Also before doing the above steps you can try power off device then while the device is still off hold the home key while connecting it to the computer and keep holding the button so that iTunes detects the device in recovery mode, iTunes should have a popup menu that asks you to restore the device