I am stuck in bios.

[ohhmaccog]

I installed a new motherboard, cpu, and ram. I bought a prebuilt pc before this. This is the same pc I’m just upgrading. I just tried to launch my pc and it won’t boot from anything. my prebuilt came with windows 10 already installed. Do I have to rebuy windows?

 

[popatim]

no.
Your upgrade may be having issues witht he old drivers trying to run hardware that the new motherbd doesn't actually have.

As for need to buy windows again , no. At worst all you need to do is breadboard the old system together enough to boot up and then link windows to an MS count. Now when you reinstall windows you just active with your MS account inistead. Its no longer tied to your hardware

 

[relo.cart]

Your old OEM Windows will not recognize the new MOBO, so OS will not load at boot.

Try below and see if it works:
(1) Download the Windows 10 FCU 1709 ISO and burn into DVD or copy to a USB
(2) Reboot with DVD/USB and get into the installation UI
(3) When ask for product key, choose "I do not have one" and select the Windows 10 version you want to install in next page.
(4) Install Windows 10 and get all drivers set up, then see if the problem resolved or not.
(5) If problem is gone, contact Microsoft to update the product key for the new MOBO or just go buy a product key elsewhere.