Hi to every one,I would like to say a happy thing in my first post but right now is not the case

I have a win7 OS, I discover ubuntu a few weeks ago, I decide to instaled in my PC, I install ubuntu in a 70gb partition of my HD and every thing runs fine, I upgrade to 12.04
and when the instalation was running the power supply of my house switch off, when i start the computer , obuntu does not run, I have a black screen thats all, I try to reinstall obuntu and the program see a win7 partition, an ubuntu 10.4 and ubuntu 12.4. When running ubuntu from a CD I can see the HD of ubuntu 12.04 but I can not run it.

Is posible to fix it? or do I have to format the HD and install every thing again

regads santiago