Most likely you damaged the hard drive with the jolt of the "hard blow to kbd". It will have to be replaced with a new one. Recovery Disks will be needed to install Windows on the new hard drive. If you need help selecting a new hard drive and/or ordering Recovery Disks post back with 'full' model number and Product number of your laptop as listed on the Service Tag attached to bottom.
Or take it into a local PC repair shop or Best Buy,Staples,etc and ask them to replace the hard drive and order Recovery Disks from HP, if you don't already have them (It would be less expensive to do it yourself if you feel comfortable attempting it)