My hd with power but cannot detect by pc due to fall in the floor while using it. lots of important data and pics

Is this problem for an IOmega Prestige 500GB external harddrive?

While I wait for you to post in a Comment,

1) Inside that external harddrive's case, is a Harddrive just like what is used in a laptop computer.
The harddrive's case measures 2.5 inches across in width. (2 and a half inches)

The harddrive is a SATA harddrive. (Serial ATA)

At one end of the harddrive is a series of connector pins. These pins plug into a female connector, or receptacle.
The receptacle is called an Interface.

http://www.allpinouts.org/index.php/Serial_ATA_%28SATA,_Serial_Advanced_Technology_Attachment%29

The Interface will have connections for Data, (Information), and Power. (Socket holes that match the pins on the SATA harddrive)

In the link above the data, and power connections for the Iomega external harddrive, will probably be a combined unit. As shown in the 8th illustration down, in the above link.

The Interface can be soldered directly to a circuit board, (PCB, or Printed Circuit Board), or will be attached to the circuit board through wires.

Usually it is the circuit board that is the problem. Components burn out, or circuit traces on the circuit board are burned apart.
(Think of a circuit trace as being a very flat, thin copper wire)

There may be a situation where the harddrive itself has come loose from the Interface. Doesn't have to be very loose to make a bad connection, resulting in the external harddrive will not work.

My proposed solution:

Open the external harddrive's external enclosure, (Case), and see if you can see any readily apparent visual signs as stated above.

No visual signs that show you that you can just plug the Interface onto the harddrive, making a tight connection?
Or plug the harddrive into the Interface, if the Interface is soldered to the circuit board?
Or no obvious signs of blackened spots on the circuit traces?

It could be that one, or more I.C.'s are bad, and are not readily visible.
(I.C. = Integrated Circuit)

Weigh buying a used Iomega Prestige 500GB USB 2.0 harddrive, and use it's circuit board, and external enclosure, against what a professional recovery service will want to recover your data.
Not trying to be trite. Am asking you to weigh the costs.

One place that came up in a search just now, that is supposed to have used Iomega Prestige 500GB USB 2.0 external harddrives,

http://www.amazon.com/gp/offer-listing/B001D7REIK/ref=dp_olp_used?ie=UTF8&condition=used


How to open the external enclosure:

Remove the external harddrive from the stand. Remove labels for access to screws. The screws will probably be Torx screws. A star shaped recess in the screw head,

http://en.wikipedia.org/wiki/Torx

May be Philips head screws, but I'm betting on Torx. (Probably metric Torx also)
You should be able to find a cheap set of Torx screwdrivers at an auto parts store. Perhaps just the bits to use in a 1/4 inch nutdriver.

Once the screws are removed the internal parts slide out of one end, or the case comes apart in two halves, and the ends come off.
(Internal parts being the harddrive, and circuit board)

Not a very professional,approach, just for an added source of opening an external harddrive's case,

http://www.youtube.com/watch?v=hQ_vjyvK28A