Hi,
I bought a used Toshiba L655 laptop. Microphone was not working. It had Windows 7. I tried going to Manage Audio devices and no microphone appeared. I know the computer had a built in mic. So I tried the following:
'''“Start -> Control Panel -> System and Security -> Find and Fix Problems -> Hardware and Sound -> Troubleshoot Audio recording”. The system found and fixed the problem for me.'''
Good luck