Usually external HDs are plug and play. However, dId it come with setup instructions? If so, were these followed?

Does it have an on-off switch?

Has it worked for you previously? If so, try this:

Shut down computer.
Unplug external HD.
Re-boot computer.
Plug in external HD and see if it is now recognized.

Have you tried connecting it to a different computer?

After working through my suggestions, please report back.

kudzu, will do, I added this just this morning, so it has never worked before for anyone. I do not have a different computer, but will give your suggestions a go. This is so confusing, there actually were NO English instructions, I found the plug and play info in South East Asia instructions, tho they are in English.
Just as you have written, for Wiindows,
Make sure the HD is connected to the computer using the USB cable, check
On the desktop double click My computer, check
Double click the icon for the Toshiba portable HD, nada, cuz it doesn't show up.

I am figguring there should come a screen with info on it? after the HD is acknowledged? with some instructions?
It also speaks of if you need help go to backup software interface? What the heck is that? I am so illiterate about this stuff, will try your suggestions in a bit and get back here. thanks so much for assist.

How old is your computer? What is the operating system? What is the size and model of the new Toshiba drive? Are you plugging the USB cable directly into the computer instead of a hub?

I have several external hard drives that I unplug frequently. When I plug them back in, they are always recognized within a second or two. When you open up "My Computer" what do you have listed for drives, both removable and non-removable?

Ok fella here goes, puter is old by standards I guess, but have XP, which I forgot to tell you I had, also this is what shows for the devices for removable storage, 31/2" floppy disk, A
Dvd Rom D, and local disk c of course is permanent.
I followed your lead, nothing still, there is no off switch, just a lite that is on, and I did plug directly into puter this time around, size is 500 GB, guess the Staples fella figgered that was plenty, I didn't ask for humougous one, just average, and told him OS was XP, was certain it would work for me. There is no modelnumber etc, just listed as 500 GB +go+ is all I can see here. USB 3.0 and 2.0 in a little box on front. As you can tell I am green as ST. Patricks beer on this, maybe this was my problem a year ago, and because I took the other one back, never pursued the end result, instead, I went to USB drives. they do work!

Exactly how old is the computer? Is it possible that it only has USB 1.1? USB 2.0 started being made available in about 2002 and later. It could be an incompatibility issue if your computer is 10 years old or so.

Do you have a friend with a computer you could plug it into to see if it is recognized? (It won't do anything to change your friend's computer as it is the same as simply plugging in a thumb drive.) If it works with another computer, at least you will know that the fault is not with the drive.

It does happen, it happened to me, the icon didn't show when I hooked it up. My CD/DVD drive did not show up either. It's been so long ago I don't know what I did to get to show. I do know I kept googling until I found help.

Computer is not over 7, and I am stretching it at that. Believe it might be 6. Sure, can try it with someone else's computer, and see if it shows, good idea, but if doesn't then what? do I return the HD and forget about it again? Or, the alternative is a new machine, and I sure am not ready for that, I want you young fellas to get all the bugs worked out of Windows 8, so I can breeze right in like I know what I am doing!
Will try and do the deed, and let you know ASAP.
As of right now, won't be able to do the deed til Wed., I am not going anywhere til then. But I will get back.

Ok, report back after you try it with another computer and we'll go from there.

Shaddy, I have an older XP computer, about the same age as yours. I have two external hard drives and both of them are recognized and work just fine. There's a story about why I have two, but won't go into that. Anyway, one of mine is the Iomega, which I've had several years. The other one is the Western Digital My Book Essential. It connects by USB (3/2) and both of these also have an AC power plug. Both work just great, and I would recommend that you try to find one of these. They come in different sizes, so I'm sure there is a 500GB available. I also have a "portable" Toshiba which I use with my Windows 7 laptop. It has just the USB connection. I'm wondering if the lack of an AC plug is causing your problem.

grandms-
In the last 5 years I've bought probably 5-6 external HDs of the type we are discussing here -- including 3 Toshibas -- and they all took their power through the USB connection, not an external AC cord. I do have one that requires two USB cords, but it's been a long time since I had one that required an AC cord. My most recent purchase was a 1TB drive and that still only takes a single USB cord.

The only reason I brought up the AC power was the age of her computer; just wondering if there was a connection there?

What make and model is the computer?

It is (slightly) possible that the power supply is not up to the task. I too have 2 external drives with their own power but they are ancient, not sure to many get built with their own power connection any more.

Shaddy RIGHT click on Start
click Explore in the pop up

Look on the left side nearer the bottom in the new window to see if your external drive is listed - probably as E: or F: but wait a few seconds after plugging in before doing this to allow the computer time to access the drive.

one possibility I will mention is that if this usb plug was disconnected from the pc with out using the safely remove icon in the bottom right of the monitor it very well can cause a corruption and cause it to no longer be recognized.
It is a must to use the safely remove icon for anything plugged into a usb port on the pc.

How do I safely remove a USB device from my computer?

My laptop looses track of a usb hard drive, when I eject it, its ejected forever I guess. Until I plug it in and then restart the computer.

Maybe search for new hardware in device manager might prompt it into finding it.

My understanding is that the risk of file corruption happens only if the external device is in the middle of a read or write operation. I rarely use the disconnect step myself, but I do wait until reads and writes are done and I close whichever programs were so involved.

Maybe that's not the best practice but I've never had a problem.

A shutdown before disconnecting is always safe to do.

sorry for the delay people, things got out of hand at home. Wanted to touch base and let you know I got the darn XHD to work, I had been plugging into the front USB ports, and of course, over time, they had become used to a degree, and found slipping the new port into the previously UNUSED ports on the back of the machine worked their magic, and I do have acknowledgement of the XHD now. Many thanks to all of you for your responses, and for the insight that made me realize it probably was something simple, and sure enuf, it was. Thanks again folks, off to do my thing now!