I honestly have only passing knowledge of it, but my understanding is that Open Build Service is more for sharing software whose source code you are allowed to distribute. If you aren't looking to distribute at all, the solutions other users suggested might be better.
There's also a way to create an APT repository entirely on your own system, without a web server, which I haven't tried myself, but a DuckDuckGo search found this: https://help.ubuntu.com/community/Repositories/Personal
Can you be more specific about what happens when you reboot? Does it go to blank screen, a blinking cursor, or just shut itself off? Does the operating system start and just get stuck somewhere in the boot process, or does it not even get that far?
I think F12 is the BIOS key, if that helps. If it attempts to boot the operating system, you can press one of the arrow keys to see the boot log.