Okay so this external disk has been working well so far until now. My operation system is Windows 7. The disk is a "iOmega eGo Encrypt Plus, Model: 31869600":

The led works fine:


This disk, as the name says, is encrypted. So, basically, when you first plugged the two USBs in, you had to open the IOMEGA (I:) 15,8 mb disk that I show here:

Then, when you entered that, you had to install the setup that appears here, and the 32/64-bit installer that was in the folder "install":

You'd end up installing this program:

When executed, you'd get this:

There I entered the password (that is already set because I set it), and I'd get a "successful inicialization" message, and then a new disk/partition would appear that had around 500 GB. But now that does not appear. Of course, I don't want to lose the data I had in the 500GB disk, and I don't know what to do, does anyone have any idea? I'll be waiting for the answers, and thank you so much!

Quite possibly the drive inside the enclosure has developed issues.

First thing I would do is to remove the drive from the enclosure and check that thoroughly.

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I have, but the led the disk is rotating well and the led works as it should.

I don't think that's it, either. I have discovered this now:

Before using the key, I have:
http://i63.tinypic.com/ereoow.jpg you see the 465 GB (500 aprox) disk is there.

Disk 1
Unknown Not assigned


After using the key (both disks dissapear for 1 second, but then):
http://i63.tinypic.com/2zzi1dj.jpg

Disk 1
Basic Not assigned

So, it does recognize it but it is... not assigned? it seems. Does this mean my data I lost? I do need the data. And how would I "assign" it?

Don't even think of trying anything like this as the most likely outcome is you would lose all your data permanently!
As has been mentioned the drive inside the enclosure has probably developed some problems.......data corruption or some bad sectors are likely? Or perhaps it got dropped?

First I would say is you need a full image of the drive. A backup! Even before cloning I would check the general condition of the drive media heads etc and then work out a plan of action.
Then you could use your key and then run a tool on the 'Disk 1 Basic Not assigned' partition and check a few things. Dmde or Testdisk might be useful tools here to search for the unencrypted partition. If you are very lucky at this point you might find a software recovery program can be used to extract your important files to another drive.

All of the above has its risks so if the data is really important you should approach a professional.