Since its just a few days before Windows 10 free installation expires, I decided to upgrade again anyways even after it nearly destroyed my PC. Will there still be an boot menu OS selection if my PC is already running Windows 10? I have another Windows 7 Professional installed on another partition on the same drive and if ever Windows 10 fails me again, I'd prefer to go back to my other Windows 7 OS.
Windows 10 does not have a boot menu like in windows 7 which comes up right after the BIOS loads. You have to partially boot the OS to access the boot menu. Windows 10 is pretty stable and I'm pretty sure it wont mess up your PC as you fear it might. The upgrade is now a "Recommended" update rather than a compulsory update. The rest is up to you. Always create a backup of your PC as it may serve you well one day. Cheers!