Since you neglected to say, I'm assuming that you're using Ubuntu. If not, check the state of your X.Org X-server drivers.
Somehow your installation has lost the I915 driver. You should have several file with i915
in their name. Here's what I see on my system:
locate -b i915
(You won't have the /usr/src/
files unless you've installed the development libraries.)
Anyhow, open the "Ubuntu software center" in the Applications menu, and pit "i915" in the search box. Select the video driver (the one without the debug symbols), and install it. (Or re-install it if it's shown as already installed.) Then reboot (so the driver will be loaded), and see if that helps,