Ubuntu boots into tty1 after driver downgrade

view story

http://askubuntu.com – Earlier today I downgraded the driver for my nvidia 240 GT from version 310 to version 304 using ubuntus "additional drivers" utility. After the install I rebooted but instead of opening unity and allowing me to login it booted into tty1 instead. After using the "startx" command I got the message, "nvidia: API mismatch: the nvidia kernel module has version 310.14, but this nvidia driver component has version 304.43." What can I do to solve this? (HowTos)