Mic not detected on Sony Vaio All-in-1 PC

My friend has a Vaio All-in-1 PC, about 1-2 years old, running Windows 7. She'd been using it to digitise some old analog cassette music last week, plugging the cassette player headphone output into the mic input on the Vaio. This was all going well.
Today however it seems that the built-in mic on the Vaio is not working/recognised - e.g. Skype does not list any microphone devices, and the Sound control panel applet only shows a disconnected Bluetooth audio device (neither of us know what that could be). There are no other microphones listed on the Recording tab.

Audio output is fine - Realtek speakers are listed in the Playback tab, and media playback is fine.

My friend fears that she may have damaged the sound connector by pulling out a cable rather violently last week, but I have no idea if that could have caused this sort of problem?

I've tried downloading and installing the latest audio drivers from the Sony site, but the setup program spends several minutes "initialising" before disappearing completely without appearing to do anything. I'm reluctant to uninstall the current drivers as my friend doesn't have any of the CDs that came with the PC, so unless I'm confident that the downloaded audio drivers will install I don't want to leave it in a state where even audio playback isn't possible.

Does anyone have any suggestions for what we can try next?