My son accidentally bump my laptop and the portable HDD fell to the floor while I'm transferring files. How can I get my data back?
If the drive is still working in some form - e.g. the drive is still spinning (you will be able to feel this when resting your hand on it, it will be vibrating just after you have plugged it in) - then I recommend buying a copy of Spinrite. If anything can still be read from the disk, Spinrite will certainly do so.
I used it a while back to recover my laptop's hard drive.
If it is not spinning at all, your only recourse is to send it to a specialist recovery service but this will cost a lot of money.