Seagate HD not detected

I have been trying to figure this out for two days now... I have a Seagate FreeAgent Desktop 500Gb external that I can not get my laptop to recognize in any way.
I have used this hard drive on many different computers with different OS's recently with no problems.
I have tried 4 different USB cables, checked all USB drives to make sure they are operating correctly, the HD is functioning normally, no strange sounds, not running hot, lighting up correctly, etc.
The computer does not react in any way when the HD is plugged in to the USB, nor does the HD show up in any way in My Computer, Computer Management, etc. It's like it just doesn't exist!
I know that the cords I've tried are good (they work for other items), I know that the HD worked perfectly fine on my friend's computer with XP a few days ago, but would not work on a different computer with XP a couple days before that (exact same problem, not detected in any way). I have not been able to test it on my bf's laptop running XP as we just moved and his power cord is currently MIA.
I am running 7 and am sure this is the problem... I just don't know how to resolve it without the HD being detected in SOME way!
I have been searching for solutions and tried many different ways of locating it on the computer, but will take any suggestions anyone has... I have a hard time believing this HD is broken when it hasn't given me any other signs of a problem...

Golden said:

I'm not sure from your post whether you have done this, but have you tied other USB ports on the computer? Or is that what you meant by "checked all USB drives"?

Yeah, sorry for the crude terminology... :) I most certainly meant ports. All 4 are functioning perfectly fine.

Unfortunately this is how it appears both normally and with the HD attached.

It's an understandable question I suppose.
The power adapter appears to be powering up the HD the same as it always has, which is correctly. Unless something has happened outside of my knowledge between now and the last time it was successfully recognized (by a different computer), it is functioning.
I currently don't have any way to verify this until I get my bf's computer running correctly and can check to see if it recognizes the HD (of course we get the power cord located for it and discover that his former roommate used it a little too much on sites he hadn't ought to of, so now I'm dealing with some real nasty viruses on that end...

Actually, I use my touchpad mouse... usually not on an even enough or large enough workspace to use a USB mouse. However, I do know that support is turned on and I regularly use the ports for other items. I just used a flash drive on it this morning to transfer some files from my bf's computer in case I have to re-install XP for him. Also, that was the first thing I checked when I realized there was a problem, then I checked the USB cord.