I was installing Ubuntu 12.04 server edition and after it detected the network interface it stopped at a blank purple screen. The install hadn’t hung because characters appeared in the bottom grey bar when you pressing any keys on the keyboard. Also you can switch to a different terminal.
The solution was to set the nomodeset in the boot options.
On boot, select the language and before pressing on one of the options such as install press F6 and select nomodeset from the menu. A ‘X’ should appear next to the menu item to say it has been selected. Press escape and continue as normal.