Usually when you power on a system, you'll see a "splash" screen. It will say something like "press DEL or F2 to enter the BIOS" or words to that effect. You'll also like see an option for pressing F11 to manually select a boot device.
In your situation, try DEL or F2.
Do you know what CPU is has? If you access the BIOS, you should be able to determine that, as well as how much memory you have. Both would be useful.
It will also help verify whether Windows 11 will run properly on it, or not.
Two tutorials were linked above. One for Windows 10, the other for Windows 11. Just follow one of those.
You never answered regarding the approximate age of the system.
We can't help you bypass a password.
You could wipe the system and perform a full clean installation of Windows and whatever games/applications you want.
From our sibling site:
https://forums.tomshardware.com/faq/windows-10-clean-install-tutorial.3170366/...
That motherboard is perfectly fine with your desired CPU. There are certainly others that have better VRM and heat management features, but as long as you properly cool your CPU and system you'll be fine.
I would not overclock with this motherboard.
The rewriting may have been the problem. Did you mention any specific game names as part of the build?
New users have some limitations.
https://forums.pcgamer.com/threads/limitations-on-new-forum-accounts.118878/