1TB transcend is healthy in disk management but in my computer only show the drive letter

I suggest you check carefully the way that unit is connected to your PC. There could be a power deficiency, according to your symptoms.

Many Transcend (and other makers') 1TB "portable" drives that are intended for use with laptops today are designed for use with USB3 ports, and say they also are "USB2 compatible". Now, a USB3 port can provide power at 5 VDC up to 0.9 amps, and many modern "laptop external drives" will work just fine with that. But the older USB2 standard had only up to 0.5 amps available, and there are almost NO external "portable drives" that can run with that power limit. Typically what happens if you plug one of these drives into a USB2 port (OR even if you use a USB3 port but only use a USB2 cable) is that they light up and appear to be working, even to the point of appearing in My Computer. BUT the moment you actually try to use them to read or write anything, they fail. That is because the power required to run the motors to turn the disks and move the heads is more than a USB2 port can supply. Your symptom description sounds a lot like that.

So, first check these items, because they all have to be right to get this working.
1. To connect the drive to your computer, use only the USB3 cable that came with it. I expect you did not also receive a separate power supply "brick" with the drive. Look inside the USB3 cable end that plugs into your computer's port. You should see a row of four contacts across the front, PLUS an additional five contacts farther back. (A USB2 cable has only the four across the front.)
2. Check the computer's USB port. IF it is designed for USB3, it also will have four contacts in one row and five in a second row.
3. IF your computer appears to have a real USB3 connector in its port, verify that the wiring from it to your mobo is plugged into a real USB3 port on the mobo.
4. IF that all is correct, check the USB device drivers you have installed under Windows. Some systems have only USB2 drivers installed, and those may not operate a USB3 port correctly.

If some of those checks disclose that you are trying to use this device on a USB2 system, that's your problem. Although this drive is "USB2 compatible", what that means is that it CAN communicate with a USB2 port BUT only if it is provided with the USB3 level of power, and no USB2 port can do that. So, what can be done? I know of three options.

A. Look around in computer shops and used parts places for an unusual cable for older USB2 external "portable drives". Those came with TWO USB2 connectors on one end of the cable, and you had to plug BOTH of them into separate USB2 ports to give the drive enough power. Using one of these instead of the USB3 cable that came with your unit might get you enough power to work, but the data transfer speed will be the slower older USB2 rate.

B. Buy and install an add-on card in one of your computer's PCIe slots that creates real standard USB3 ports and use them for connecting your drive.

C. This is another way to provide the power needed, and I've done it with success. Buy a USB3 Hub that comes with its own power supply "brick" you plug into the wall and into the Hub to give it the power its ports can supply to the devices. It also comes with a USB3 cable to connect to your computer's port, and it does not matter whether that is USB2 or USB3. (Well, it makes a bit of difference - see later.) In choosing your Hub, note that the power supply that comes with it must be able to provide 5 VDC at 0.9 amps for EACH of its ports. The tricky thing here is that many of them come with a 12 VDC power supply brick, and the Hub converts the voltage. In that case you need to concentrate on the WATTS the power brick can deliver. 0.9 amps at 5 VDC amounts to 4.5 Watts per port, so ideally a Hub with four ports should require about 20 Watts. At 12 VDC, the power "brick" should put out 20 W, or about 1.7 amps or more. If you get one of these, here's how to hook it up. Plug your Transcend "portable drive" into one of the Hub's ports, using the USB3 cable that came with the drive. Plug the power supply brick into the Hub and into the wall. Use a USB cable to connect the Hub to a USB port on the computer. This will give your drive the power it needs, but the data transfer speed will depend on the details of the connection between the Hub and the computer, as follows. IF the computer's USB port is USB2, OR if you use a USB2 cable there, the system will operate at the slower USB2 rate. It can only operate at the new fast USB3 rate if ALL of the components are USB3 - that is, drive, drive cable, Hub (with power on), cable from Hub to computer, and computer port.