MAC Bootable Flashdrive Error

So I got this mac from my dad and i need to upgrade it for school, its a mid 2009 gen and it have mac mojave compatibility. So i made a bootable drive with mac mojave on it and i restart my mac and hold alt to boot to select my flash drive to boot (now here comes my problem). When i select my drive to boot, it starts loading and after a few seconds the screen goes black and the mac restarts, telling me that and unexpected error has occurred, restarting mac. When the mac goes to the home screen i get a long error message but i dont understand anything. So if anyone can shed light on this, if you need me to send the error message let me know. Please this is urgent.