IF you plug an external Hard drive in Computer by USB and you cant see it in My Computer , What is exact steps fix this issue?

This is the problem of disk mangement section so, check the options clearly. if it is not sure to use then once check the device may it's functions damage. Or this may be the problems of some threads so make it clear what is the problem. 

قبل كل هذه الاشياء يجب التاكد من سلامة رابط التوصيل بين الهارد ديسك و الكمبيوتر ثم التاكد من سلامة الهارد ديسك,ان كان يحدث صوتا عند التوصيل فهذا يعني انه يعمل بعد ذالك يمكن التحقق من الدريفرات و شكرا

solution1 : un install driver from device manager :

 Device Manager*From there, expanded Universal Serial Bus controllers. * There's a whole list there of all different devices and stuff, there u may see "unrecognized device", or something like that.  opene that and go to the Drivers tab, and there, you uninstall the driver. It gave you a warning before that u delete the device from your computer, so if you get that, don't worry, just do it. (*After you uninstall the driver,just clicke the button to update drivers... it may work if not do second step

solution2: Change the Drive letter : from Disk Management, in the top section where it just says the list of your devices, right clicke on the hard drive, and clicked on Change Drive Letter and Paths... 

* From there, clicke "Change".  :, you have to change the drive there to another one and then it'll work. It did for me! and worked this solution

IF

 this computer is old one the issue is USB ports don't provide enough power to run the Drive.this

These Externel Hard Drives are powered by a USB Port.Some USB ports don't provide enough power to run the Drive. Use a USB port on the back of your PC. A powered USB Hub may also be helpful if your PC doesn't supply enough power" 

Go to Computer >click right > manage > Disk management :see if there's a partition need a letter to assign , if not, give it the letter. if you can't see your driver there, may be the corrupted hard disk.

go to 'run'

then type 'cmd' enter

type 'attrib -s -h -r /s /d G:\*.*'

make sure that G: in the above command is path of your external device connected to USB. if it is other than 'G:' type the letter in place of 'G' in above command

قبل أن تفعل هذه المرحلة يا أخى عليك بالتأكد من أن الهارد الديسك قرىء اولاً على الجهاز وتعرف هذا عن طريق سيت أب الدوس وجعل الهادر يكون ساكند وشكراً

The power of the usb cord might be less and need to upgrade it to the standard of the drive.

on my computer leftclick go to  manage then try disk management

The drive may need to be assign a letter.

This can be done from the disk mangement section.

Right click Computer(or My Computer if winxp)--click on manage--click on disk mangement

Check if there is any disk1.. (Disk0 is usually the boot drive disk)

If yes, right click the right pane and click on add drive letter.

It may also be that the driver for the drive is missing. you may confirm this from the device manager.

If there is no disk1 in  the disk management, then it might be that your antivirus is blocking.

If antivirus is not blocking then the disk is corrupt

CHECK THE DRIVE IF THE JUMPERS ARE WELL FIX AS MASTER OR SLAVE