I installed ubuntu 11.10 and after a while it get damaged and I install another one in another partition . After I boot to the new one I delete the old one ( I format its partition ) . When I restart I couldn't boot . What is the solution ?
Without error messages or more detailed explanations of what happens, it is really hard to tell what the computer is doing. However, a possible cause of errors is that your boot loader (GRUB) cannot find the old version of Ubuntu and fails while it is trying to create the boot-up menu.
You can try to recover the system using various commands from a LiveCD, but if you don't want to deal with all that, a simpler solution is to just install the new one again. It gets you up and running with the least amount of fuss.