When i just turn the power to my car on, a part under the hood starts getting really loud, and starts shaking but i don't know what it is

im absolutly sure your car needs a new owner... lol

In such cases: consult a workshop. There's an awful lot of things that could be noisy under the hood.... ;-)

try to describe the part and its location I might then be able to help you out better. Many things could cause this to happen, and do you mean that your car isn't running but you have the key in the on position and it makes the noise.

sounds like a belt in the middle of the engine