Windows 7 Installation Error: BOOTMGR is Missing

At last, the BOOTMGR nightmare is solved!

After almost 15 hours of desperately looking for a solution, I finally managed to install Windows 7 on a newly assembled PC that always threw this message on my face.
My girlfriend asked me one Saturday night to install Windows 7 in a new desktop PC in their office. She does not have a Windows 7 installer CD so I made a Windows 7 USB Installer using Unetbootin.
I've done this many times before and I'm confident that it will work. But to my shame, it didn't.
The newly assembled PC always returns a dark screen with the annoying message for me. BOOTMGR is missing.

The First Solution for the Missing BOOTMGR Problem

I Googled the problem and I learned that the problem resides in the hard disk of the PC. There is something wrong with how the hard disk is configured.
I thought, maybe this is one disadvantage of assembling a PC - some hardware are not properly configured.
The solution that people on different forums suggested is to use the Windows Installation Disk and choosing the Repair option. There goes a problem because I do not have a Windows 7 Installation DVD. All I have is a bootable USB Flashdrive and a Windows 7 iso.
This made me think of another solution - a more probable solution.

Solving the Missing BOOTMGR Problem Without a Windows Installation Disk

I cranked up my brain and I thought, "If the hard disk is not properly configured, then I have to configure it." The problem is how to configure it. I can't reach it and I cannot reformat that hard disk.
Or, can I?
I need a way to configure the hard disk and access it. Eureka! I need a portable OS.
I then downloaded the smallest linux OS that can be installed and run on a USB Flash Drive - 50 MB Puppy Linux.
Using Unetbootin, I made another bootable USB Flash Drive. I now have two bootable Flash Drives, one for Windows 7 and another for Puppy Linux.

Using Puppy Linux to Format Hard Disk

I plugged my Puppy Linux bootable USB Flash Drive to the PC, hit F8 and chose that USB Flash Drive as the boot device.
I'm now inside an Operating System that runs completely on my Flash Drive!
First things first, click the Menu (Start button) then System and finally, GParted Partition Manager.
Format the hard disk as an NTFS device and click apply.
The hard drive is now ready to be used. However, this is not true in my case. The bootable Flash Drive with the Windows installer is still not working.

Copying Windows 7 Installation Files to Hard Disk

As my thinking approaching its threshold, I figured out that I can copy the Windows installation files to the hard disk and install Windows from the hard disk itself.
But how do I copy files on Puppy Linux?
I looked around and found the icons for the USB Flash Drives and Hard Disks just above the Menu button. I opened them and copied the files by highlighting them and dragging them to the hard disk window.
I then restarted the PC and booted from the hard disk.
The appearance of the Windows logo on the PC's screen made me scream, "YES!"