Hi, It sounds to me that your hard drive was damaged when you dropped your computer. You probably need to replace the hard drive and install a fresh copy of the operating system. If you don't have a disk you can probably get one from Dell for a low cost. I am providing a link on replacing the hard drive. Hope this helps.
http://blog.parts-people.com/2014/10/28/dell-latitude-e6440-hard-drive-removal-and-installation/