how to format a SD card that windows is unable to complete using cmd 
 open a command prompt and write the following codes.
NB/ you must insert your SD card before writing the codes 
1. type diskpart
  there will be dialog box popping up accept to continue. after accepting, there will be another command prompt popping up. attached the following codes to the new CMD window .

Open command prompt and type the following commands..
1.diskpart- this navigate you to another command prompt dialogbox.
2. On a dialogbox type 
      List disk. 
3. Select disk you wanna format to proceeds with same e.g "select disk 1" the press enter to continue.
4. Type "clean" then press enter.  
5.type "create partition primary" then press enter to continue.
6. Type "select partition 1" then press enter.
7. Type "active" then press enter 
8. Type "format fs=ntfs quick" then press enter.
  There will be progress with formatting, wait it upto 100% and your disk will be ok.  
NB: check your cluster sizes and file attributes...