reinstallation of Ubuntu OO on AC 100

I have installed Ubuntu OO on AC 100. Everything was O.K. - everything without speakers and Flashplayer was working. I tried to install nvidia driver too, and this was not a good idea. when i tried to uninstall it, i probably removed the only graphic driver, because after reboot everything ends in splashscreen and unity doesnt start.
I tried also reinstall ubuntu from SD card, but system boots from emmc and installation couldnt start.
When i tried to download "preinstalled-desktop-armel+AC100.bootimg" with NvFlash on partition 6, i had no success.

I have this idea: when that .bootimg on partition 6 is, it can start installation from SD card. And I must overwrite the current content on this partition "LNX" with this bootimg.
Am I right?

Download of bootimg is not successful. terminal shows only : Nvflash starting ... and nothing more for a long minutes
Need I format this partition first?

Or anything else?
Sorry, I am not IT expert, only a doctor...
Thanks for answer and help