The sites owwm.org and vintagemachinery.org (the latter site formerly known as owwm.com) are separate sites run by separate people. But many people use both and they are commonly confused; that's part of the reason why owwm.com changed its name to vintagemachinery.org. Both sites are entirely run by volunteers and at the expense of the people running them. Each represents thousands of hours of effort by those people. Neither site can afford to use expensive hosted services that would improve reliability, so you have to accept that the sites will occasionally be offline.
Each of these sites have separate Registration and Log-in procedures. You can register for Vintage Machinery here
and for owwm.org here
. It should also be noted that the WIKI-Knowlege Base has its own separate registration which can be found here