You don't say what kind of computer, or if you want to preserve the ability to return to windows, but assuming you are willing to throw everything to the wind and start fresh you can simply delete the three partitions (21 GB, 1 k, 19 GB). Understand this will PERMANENTLY destroy all data on your hard drive, including any recovery partitions or manufacurer partitions.
Recovery of the drive will likely be problematic. Depending on exactly when the power went out during the process there could be nothing to recover, or a lot to recover. If there was nothing of value there the best advise is to completely wipe the drive and start over.
Highlight each partition and choose "Delete" then you will need to add one or more partitions for ubuntu and complete the install process. If you are starting the ubuntu install from scratch you can simply tell it to do a clean install and use the entire drive.
Hope this is helpful.