Gentoo does have systemd, actually—package sys-apps/systemd—and there are optional sections in the install documents that explain how to go about using it as your primary init. It’s an officially supported configuration, just not the default.
(But yeah, as for the main problem, sounds like hardware—RAM, your primary hard disk, or the disk controller on the mobo. Start with The Bleeding Obvious and make sure all cables are solid in their sockets and all the RAM is properly inserted.)
I will have to remember not to use that command anymore. 'Scuse me while I clean up the hairball . . .