Which driver did you install when you did the update? The one from Microsoft's Update, Sigmatel, or from Dell's website?
You might just try to roll back the driver, I have a system that I installed a video driver from Microsoft and it did all kinds of bad things.
Control Panel > System > Hardware tab > Device Manager > Sound, Video, and Game Controllers > right click on the audio drivers and select properties click on the Driver tab and select Roll Back Driver.
See if that works. You probably installed a driver from Microsoft when doing updates that is not playing nice with your system.
Cheers
Rob
The answer is always "PEBKAC!