Comment 22 for bug 632046

Hope this offers some insight... although I was unable to get any support info for UBUNTU from Panasonic (no surprise) the fix offered for Windows 7 shows that they still do not have a good handle on the issue, but it points toward being a hardware bug linked to use of the Fn-F4 or F5 or F6 (Mute & Vol.) buttons. Once mute is used during certain (unknown) conditions, it will not unmute the speakers.
Panasonic stated that certain (unknown) updates pushed to Windows 7 (and Vista, and XP) will trigger the issue. Their "fix" was to try rolling back to a time before the last updates were applied, or to completely remove and reinstall the drivers "in a specific order". What follows is the chat window contents for my Windows 7 support call and the supplied steps to resolve the issue. Maybe it will help (a bit out of order, as I moved my mention of Ubuntu to the top):

You: OK, that should keep me busy for a while. Thank You. I have a friend who has the same issue with the same model laptop, but he is using UBUNTU. Do you have a fix?
Jeev: Not for uBuntu.
You: weird that it seems independent of the OS. Are you familiar with the actual problem's cause?
Jeev: It seems like after some Microsoft updates when the sound functions FN+F5 or F6 is pressed, it happens. Which MS updates is hard to tell. Hence the roll back.
You: Yes, that seems to fit. Thanks again.

Jeev: The instructions supplied here, will guide you through restoring the sound functionality for the laptop.
Jeev: This will apply to laptops which have lost sound capability after using the mute feature or installed service pack updates.
Jeev: Files to download:
Jeev: Hotkey Driver
Jeev: Hotkey Settings
Jeev: Hotkey Appendix
Jeev: Please visit the Panasonic US Support website to down load drivers. The website requires an account to down load drivers. You will be able to fill out the registration form on the main page to obtain a user name and password. Once registration is completed you will receive your user name, and password via email.
Jeev: PANASONIC US SUPPORT WEBSITE:
Jeev: www.panasonic.com/toughbook/support
Jeev: Please use the following steps to restore the sound functionality.
Jeev: 1. Open Add or Remove Programs, to access Add or Remove Programs
Jeev: a. Click on the Start button then [Run…]
Jeev: b. From the Run command line type "appwiz.cpl" and click [OK] to continue.
Jeev: 2. The Add or Remove Programs window will appear.
Jeev: a. Select Hotkey Settings, and click on the Change/Remove button. [If the Hotkey Setting is not listed continue on to step 3]
Jeev: b. The Confirm File Deletion will appear, [Do you want to completely remove the selected application and all its components?]
Jeev: c. Click on the [OK] to continue
Jeev: d. Install Shield Wizard window will appear. Click on the [Finish] to continue
Jeev: 3. Add or Remove Programs window
Jeev: a. Select Hotkey Appendix, and click on the Change/Remove button. [If the Hotkey Appendix is not listed continue on to step 4]
Jeev: b. The Confirm File Deletion will appear, [Do you want to completely remove the selected application and all its components?]
Jeev: c. Click on the [OK] to continue
Jeev: d. Install Shield Wizard window will appear. Click on the [Finish] to continue
Jeev: 4. Add or Remove Programs window
Jeev: a. Select Hotkey Driver for Panasonic PC, and click on the Change/Remove button. [If the Hotkey Driver for Panasonic PC is not listed continue on to the next step 5]
Jeev: b. The Confirm File Deletion will appear, [Are you sure you want to completely remove 'Hotkey Manager' and all its components?]
Jeev: c. Click on the [Yes] to continue
Jeev: d. The System Setting Change window will appear, [You must restart computer manually before the new settings will take effect]
Jeev: e. Select [Yes] to continue.
Jeev: 5. Restart the laptop
Jeev: a. At the Panasonic splash screen tap on the [F2] button. This will bring you into the Bios setup utility.
Jeev: b. Press the [F9] function key and hit Enter > Yes to reset the Default Configuration .
Jeev: c. Press the [F10] function key and hit Enter > Yes to Save Changes and Exit.
Jeev: 6. The laptop will reboot into the Operating System.
Jeev: a. Log-in to Windows as the Administrator.
Jeev: 7. Click Start > All Programs > Accessories > Windows Explorer
Jeev: a. Click Start > Run…
Jeev: b. From the Run command line type "explorer" and click the [OK] to continue.
Jeev: 8. The Windows Explorer Windows will open.
Jeev: a. Click on My Computer
Jeev: b. Double click on Local Disk (C:)
Jeev: c. Double click on the Util or Util2 folder.
Jeev: 9. Double click on the hkeyset folder.
Jeev: a. Double click on setup.exe.
Jeev: b. The Install Shield Wizard will appear. Click on Next > to continue.
Jeev: c. Click on the [Finish] to continue.
Jeev: d. Click on the [Back] button on the top left corner of Windows Explorer.
Jeev: 10. Double click on the hkeyapp folder.
Jeev: a. Double click on setup.exe.
Jeev: b. The Install Shield Wizard will appear. Click on Next > to continue.
Jeev: c. Select [Yes, I want to restart my computer now].
Jeev: d. Click on the [Finish] to continue.
Jeev: 11. The laptop will reboot into the Operating System.
Jeev: a. Log-in to Windows as the Administrator .
Jeev: 12. Open the Device Manager, to access the Device Manager
Jeev: a. Click Start > Run…
Jeev: b. From the Run command line type "devmgmt.msc" and click [OK] to continue.
Jeev: 13. The Device Manager window will appear.
Jeev: a. Click on the [+] sign next to the System devices.
Jeev: b. Right click on [Hotkey Driver for Panasonic PC], Select Update Driver…
Jeev: 14. Welcome to the Hardware Update Wizard will appear.
Jeev: a. Select Option: [No, not this time]
Jeev: b. Click on Next > to continue.
Jeev: 15. This wizard helps you install software for: PS/2 Compatible Mouse message will appear.
Jeev: a. Select Option: [Install form a list of specific location (Advanced)]
Jeev: b. Click on Next > to continue.
Jeev: 16. Please choose your search and installation options message will appear.
Jeev: a. Select Option: [Don’t search. I will choose the driver to install]
Jeev: b. Click on Next > to continue.
Jeev: 17. Select the device driver you want to install for this hardware message will appear.
Jeev: a. Click on the [Have Disk…] to continue
Jeev: 18. Install From Disk windows will appear.
Jeev: a. Click on the [Browse…] to continue
Jeev: 19. Locate File window will appear.
Jeev: a. Select Local Disk (C:)
Jeev: c. Double click on the Util or Util2 folder.
Jeev: d. Double click on the driver folder.
Jeev: e. Double click on the Hotkey folder.
Jeev: f. Select the hotkey.inf file listed.
Jeev: g. Click on the [Open] to continue
Jeev: 20. Install From Disk windows will appear again.
Jeev: a. Click on the [OK] to continue
Jeev: 21. Select the device driver you want to install for this hardware message will appear again.
Jeev: a. Select [Hotkey Driver for Panasonic PC]
Jeev: b. Click on Next > to continue.
Jeev: 22. The Hardware Update Wizard will install the Hotkey Driver for Panasonic PC driver.
Jeev: 23. Completing the Hardware Update Wizard window will appear.
Jeev: a. Click on the [Finish] to continue
Jeev: 24. System Settings Change window will appear.
Jeev: a. Select [Yes] to restart the laptop to complete restoring the sound functionality.