Pendrive bootable by command prompt

 Step 1:
Open your PC's PowerShell or Command Promt with administrative rights.

Step 2:
After inserting your USB pendrive, run DISKPART from the PowerShell.

Step 3:
Type the command LIST DISK. The result will be as shown below:

Here DISK 0 is the hard disk and DISK 1 is the pendrive I have used.

Step 4:
In my case, the USB drive is DISK 1. So in this step, I enter the following command:
SELECT DISK 1. According to your disk number, the "1" in the command will change.

Step 5:
After the USB drive is selected from DISKPART, enter the following commands one by one:

CLEAN

CREATE PARTITION PRIMARY

SELECT PARTITION 1

ACTIVE

FORMAT FS=NTFS QUICK

ASSIGN

And at last, enter EXIT command

Step 6:
Exit PowerShell and insert your Windows 7 installation disk. Now open 'My Computer'.

Note the drive letters of both - Your pendrive and Windows 7 installation disk. In my case, they are G: and H: respectively.

Step 7:

Again start PowerShell and enter following commands one by one:

H:

CD BOOT

BOOTSECT.EXE /NT60 G:

Note the drive letters I used here are H: and G: according to my drives and these letters may be different for you.

Now your pendride has become a bootable one.