When I check Control Panel, it's not showing a microphone.
I tried to update the audio drivers but it's showing that it's up-to-date.
I am running Windows 7 Home Premium 64-bit on a Dell XPS 15 laptop.
Update will not necessarily always work automagically. Try installing drivers from DELL website.
Try uninstalling the drivers first. Then go directly to the website, DELL I guess, and install the latest drivers there.
I've had this problem before, where drivers won't update easily like they are supposed to, and like @Nux said too. For lots of Windows PC's and laptops, Windows XP as well as Windows 7 (I also have 64-bit home premium), this still keeps happening!