I was installing Ubuntu in a partition created directly from the installer, using the CD method, after the step when one set up the partitions of the hard drive, the installation crashed. After that I was trying to do it again and the same situation. After a while I got tired and turn it off, when I reboot it and tried to use windows, neither of the OS worked, it just goes into a black windows with and "_" blinking. Please help I'm afraid that my pc had died, or the windows os had been damaged, lots of important files from the university.
If your partition table is not corrputed, use super grub disk to boot into windows and compare checksums of the iso. If nothing is wrong with your iso, edit the ques. with every specific detail of your computer and check for supported hardware on ubuntu and linux kernel website.
If the installer messed up your partition table (backups, backups, where are you), try restoring it with a tool like TestDisk, there are alot of howtos on the web to help you.
If, luckily, you made backups before the installation (the whole disk backups that even backup your mbr and partition table), just restore the backups and try again (with a new iso?).
But, as you said, you have important stuff on there, use your liveCD to boot into a live (not installation) environment and get your stuff out of there first (that is if your partition table is intact)
Finally, before you try again, MAKE BACKUPS? You must understand how important they are and remember to make them before messing around risky stuff and there are enough websites to teach you how to do that.
Hope I helped :)