how to get the file used to brute force any encryption method Bitlocker as example uses AES 128 Bit encryption as default - if it was brute forced how it can be done , I mean where's the file that will be brute forced to generate the password (If I'm right that file is suppose to be the 128 keys generated from the encryption right?)
 I'm not asking about software to do this ( I'm aware that some apps uses hibernation file or memory dump file to do so) I'm asking about how to find it manually , If i deleted both previous files and stopped any administrative privileges for installing any software will it be impossible ??
If I'm understanding your question right, you're asking "How to brute-force the Bitlocker encryption without being able to install stuff and without using "backdoors" and without having the key-file (if used)?"

You can't brute-force AES-128 without the said key-file.
The reason for this is that the key file contains the 128-bit keys which are too hard to guess by themselves. If you don't have access to this file at all you can't break AES / bitlocker in a passive sense. You could still run evil-maid attacks though...

If you have access to the encrypted key file and it uses a password there is a chance you can break the encryption scheme.
The reason for this that you'd guess the password used to encrypt the key-file and then properly decrypt it and use the embedded key to decrypt the encrypted data. You can guess the password by simply trying all possible ones out until you hit the lucky one which is feasible because there are only usually "a few" passwords possible ($\approx2^{40}$ compared to $2^{128}$)

Note that the inability to install custom software isn't a restriction in the usual threat model for drive encryption. Usually it is assumed to have physical access to the drive and being able to read sectors while at rest. So one could look for a known structure to perform the brute-force attack so this is feasible (in the right scenario).

TL;DR: You can't break AES, but a password if used, so the password may be weakest point to attack.