Tried to configure and crashed Graphic interface at start-up. now stuck with no 3D
It's likely that you have caused the machine to use the backup nouvou or vga drivers if your nvidia configuration failed.
You need to reassert the old xorg configuration:
Then restart your computer to take effect. If you don't solve this issue wit this, please post your configuration and your dmesg log. Also consider posting a bug report as to why you needed to configure nvidia in such a way as to potentially make it fail.