My other question is what happens with the OS? Does windows need to be rebought if I upgraded my windows 7 to 10 for free?
No, but it requires you to have undertaken certain steps before you even upgraded. I am not sure if you can still boot your PC to undertake those steps, but I am gonna list them anyway. If you can't get your PC to run anymore to do this prep, then you're fucked.
Firstly, you need to make a bootable installation file for Windows 10. To do so, have Win 10 installed and then download a program called the Windows Media Creation Tool. Run the program and follow the steps to create a Win 10 installation file. Make sure to have a USB flash drive plugged in so the program can place the installation files on the usb drive. It's free, 100% legal and pretty easy to use. Should be plenty of guides on the interwebs too.
Secondly, write down your Windows license key. Now, there is good possibility that Windows automatically assigned you a new key when you upgraded, meaning your retail Win 7 key won't work. There are programs on the internet that can find and identify Windows product keys on your computer for you. Google it as I can't recall what tool I used.
Now, when you have your new PC all set up just boot from the flash drive, install Win 10 and activate your key once its done. Voila.