Everything was fine in the past. Now - When I try to draw a circle or ellipse, it starts out as an incomplete shape with a faint outline. If I try to pull the node over to make a complete circle it disappears leaving just the node.

How do I get the outline dark? It is at 100% for opacity and all dark numbers for stroke are as high as they go.

How can I get it to start with drawing complete circles and ellipses again?

I'm guessing you tried to manually put the circle arch's end handle next to the starting handle, from "inside" the ellipse.
Click on the reset arc to ellipse icon at the tool's control bar.
http://tavmjong.free.fr/INKSCAPE/MANUAL/html/Shapes-Arcs.html

You can use the xml editor or the bottom indicator line to see what's going on with the fills, if that's the problem.
Use the fill and stroke panel to add an alpha of 255, an opacity of 100%,
check if the ellipse you draw is not inside a group with no opacity value or on the masked/clipped part of the group,
check if the layer's visibility is on and the opacity is at 100% too.
Though I think reseting the tool back to ellipse instead of arches will solve your problem itself.

Thanks! all is good.