Mac Pro help please

[R@NDOm2508]

hi thee I am currently running El Capitan on my 2008 2.8 eight core Mac Pro but I am wanting to go back to yosimite or Mavericks I don't have any back ups with either OS X but I put Mavericks on a usb stick. The problem is my Mac won't go into recovery mode or any of the other start up utility commands to be able to format my SSD and install Mavericks just goes straight back to my normal login screen. I am using a usb apple keyboard if it helps.

Thanks in advance

 

[Hellhammer]

MOD NOTE

Do NOT run the Terminal command in the post that was deleted. It is malicious and will install malware on your Mac.