New Dell 1120 motherboard Seven beeps when you turn it on

I am replacing my dell 1120 motherboard because it failed (per dell). Seven beeps when you turn it on. I confirmed separately that that's the processor failure. anyways...I have a replacement motherboard coming. I lack experience how to proceed. My goal is to get the laptop working again and back-up my hard drive, since I haven't done that recently. Lost valuable files. Here's my question, Once I reinstall the motherboard, I assume I need to upload an operating system to make it work, or something like that. Any advice?

Jeff