It maybe the keyboard that is the issue. Try turning it off and connecting an external keyboard. Then it should allow you to log in. Once in, to see if it is the keyboard or the drivers ...
1. Uninstall the keyboard driver.
2. Reboot the computer (without reinstalling the driver).
3. When it restarts, it should reinstall the driver on its own.
If this doesn't work, you may wish to try connecting then external keyboard again and see if it works fine. If it does, then it could be the keys themselves that are the issue.
You may also want to try updating the Synaptics Driver if the above doesn't help.