Startup Repair will fix several problems, but there are some it does not seem to be able to fix. Can you boot into anything that has a command prompt, like the WinRE environment using F8 or booting to a Recovery CD or Install DVD?
When does the black screen occur, before or after the Windows Logo?
Hard to say what Ubuntu might have done to your system. It normally overwrites the MBR and removes the Windows 7 boot files, but it seems that did not happen in this case.
You might want to download and burn a Partition management software to look at your hard drive. Partition Wizard or G-Parted will usually work, and G-Parted may be on the Ubuntu DVD if you just load it for trial and not install it.