No linux boot after updating to Ubuntu 14.10

Hi,

My hack is a dual-boot Yosemite/Ubuntu on the same SSD Drive.
It worked fine before I updated Ubuntu to 14.10 (it was 14.04 LTS before).
It did the same before when it was on a HDD, and it worked.
I've reinstalled everybody on my new SSD and linux can't boot anymore since I updated 14.04 to 14.10. Yosemite still boots without any problem.
I think it's a grub problem but I don't know how to repair it.

Could you help me, please ?
Thanks

I've cleaned Ubuntu boot reinstalling 14.04LTS, it works. I made a save with SBackup, and I try again to upgrade to 14.10 Utopic Unicorn.

The problem is the same.
When rebboting on Ubuntu 14.10, the pink screen appear, after what some lines :
(there are very much lines, the screen is filed from top to bottom)

After what a black screen appear with blinking cursor and nothing else.
When I shut down the computer with the power button, the exiting screen of Ubuntu appear before extinction.

Please, could you help me !!