JackHinton :
PC-4LIFE :
Well be sure to back up your data before wiping your drive, but don't back up the OS files. Secondly, you will need to reinstall windows since you have a new motherboard and CPU. Formatting your hard drive is relatively simple, just go to file explorer and right click on the hard drive with the OS, and click format. It may take some time, that's normal.
Now this is the tricky bit. You need either an installation disc, or a 4gb USB. If you have an installation disc just put it in, boot from it and enter your windows key. If you don't have it anymore you can contact Microsoft support. If you have windows 10 then the key may be linked to your Microsoft account, in which case you don't actually need the key.
This guide explains in depth how to install from a USB/DVD https://www.microsoft.com/en-gb/download/windows-usb-dvd-download-tool
So just transfer the files i want to keep like my steam directory etc, and format the hard drive. Then replace everything and i should be good? Also i have the windows disk with the key but worried i wont be able to use it again, i dont know if it is a one time use or not. Thanks for the help, really appreciate it.
You can only use the key on one device, depending on the one you have bought. Because it's a new motherboard windows will detect that and will demand a key. If you have the key it should be fine, you can use it as many times as you want but only on one device. It will possibly think you already have an activated version of the key, in which case you need to contact Microsoft, but they will sort it out.
And, I wouldn't bother backing up applications like steam (Unless they aren't available online), not sure that would work anyway. Just reinstall on the formatted hard drive. Backup important files like word, power point etc.