1. Get a PC.
2. Install OS.
3. Copy your files over to PC.
4. Format laptop - In OS installation or in BIOS. (I assume laptop because dropped).
5. Reinstall OS on laptop.
6. (Optional) copy non-system files back to laptop from PC.
7. (Optional) download iCare Data Recovery or similar to recover files from inaccessible disks.
If the laptop still doesn't work, then there's a hardware problem, and you probably need a new computer or component.
If not a a laptop, then it's probably just one component, like the motherboard or hard drive that the OS is installed on