Keyboard emulation issue

Hello everybody!
I have an Arduino Leonardo + Keyboard library. The board is connected to the system unit with a standard cord. Under Win 7, everything works without problems: the system accepts the characters sent by Adruino (I tested through standard Notepad). What is the problem: before loading the OS, the computer does not react to the characters sent. As I checked: 1 way) I took a computer with a drive protected by TrueCrypt. When you turn on the computer, you need to enter a password to boot the OS. Arduino sends characters, but nothing is displayed on the screen. 2 way) I enter BIOS through a normal keyboard, then through Arduino I send characters. The effect is saved - the computer does not see the characters sent to it. Checked repeatedly. Question: is this behavior related to some feature of the library, or is it an Arduino Leonardo property? How to fix? Thanks!

Look at this thread for more info.