Using the USB was a mistake as HP laps and computers have an easy access recovery partition which would have done the clean-up job you wanted.
Now, your os is corrupted. I am afraid that you will need to use your recovery disks which HP asked you to create when you first set up your machine.
You may ask what shall you do if you don't have the disks anymore. The only thing I can think of is to contact HP support.
Sorry and good luck