Microsoft Windows is very stable now. No need to format Windows when system crashed. I still remember the day when using Microsoft Windows 95 / ME. Windows is not so stable and tends to crash if the applications do not running well. Boot disk is a must have to troubleshoot. I was using floppy drive and CD ROM as boot disk back then. But it is replaced by USB flash drive nowadays. How to make USB Pen Drive bootable? There is a tool called Makebootable from PenDrive that can make your Pen Drive bootable.

Makebootable
Makebootable System Requirements
Makebootable is an old application and only working on old Microsoft Windows rather than Windows Vista / Windows 7. Further more, it does not support FAT32 and NTFS file system format. So you need to format Pen Drive as FAT. I tried to use it on Apacar flash drive. I was able to make the flash drive bootable with Makebootable. 4 files (COMMAND.COM, DRVSPACE.BIN, IO.SYS, and MSDOS.SYS) were copied to it. However, I failed to make it boot. Must be setting issue else is my GIGABYTE EP45-DS3 motherboard issue (no matter I select USB-HDD or USB-ZIP). Anyway, no harm try it out as it might work for you.
Download PenDrive Makebootable here.
via: PenDrive
nice tip bro..
how about for Windows 7?
[...] have bootable 1.44-MB diskette or CD-ROM. Floppy drive is long gone by now. I still have issue to create a bootable USB Pen Drive. So the only way is use [...]