You can try this from the Panasonic FAQ.
No sound from speaker
CF-18, CF-19, CF-30, CF-31, CF-51, CF-52, CF-53, CF-74, CF-C1, CF-D1, CF-F9, CF-S10, CF-T8 and CF-U1
Operating System: Windows 7 and Windows XP
Release Date: Aug 23, 2012
No sound from speaker(s) even not muted.
The Hotkey Appendix, which is an application software of
Panasonic, should be installed to mute/un-mute speaker(s).
Once speaker(s) is muted, BIOS remembers that in NVRAM(*1). To un-mute it back, the Hotkey Appendix is required. To install the Hotkey Appendix, run setup.exe as an administrator and follow the message. The Hotkey Appendix is located at c:\util\hkeyapp\setup.exe
Please refer to following "How to set up Hotkey Appendix Utility".
Open Start Control Panel - Programs - Uninstall a program (XP: Start -Control Panel - Add or Remove programs ), confirm the Hotkey Appendix is in list.
[Except; CF-D1 (No key board), CF-U1 (Fn and R key)]
Hit Fn and F4 key simultaneously, the speaker mute icon should be displayed on the middle of screen. If no icon is displayed, the Hotkey Appendix is not installed.
Non-volatile random-access memory (NVRAM) is random-access
memory that retains its information when power is turned off.
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