When you get the blank screen, does pressing 'Ctrl+Alt+F1' get you to a TTY?
Assuming that you updated to 12.10, the most likely cause is a known bug from the update not including as default the correct linux-headers files.
If you boot to a TTY [Text terminal] and run:
that will tell you which kernel version is active, and which drivers are in use, and their package name. [ If the third cmd shows nvidia-current installed, there is no need to run the last.]
lspci -nnk | grep -iA3 vga
apt-cache policy nvidia-current
apt-cache policy nvidia-experimental*
Then, assuming you have an Internet connection, run:
If it actually installs them then remove the installed video driver and reinstall it - or another version. For example:
sudo apt-get update
sudo apt-get install linux-headers-generic
sudo apt-get install linux-headers-<uname -r> # replace '<uname -r>' with the output of that cmd
sudo apt-get install linux-source
If the 'install linux-headers...' cmd returned: "... already the latest version" then this is not the cause and we need to look elsewhere.
sudo apt-get remove --purge nvidia-current # If unable to find the installed driver's name, change to 'nvidia*'
sudo apt-get install nvidia-experimental-304
To get an Internet connection you may need to boot via recovery and activate it before dropping to a root shell.