"Cart Clearo"? "An open"? I use a Kanger tank... not terribly familiar with all the terminology. It had been working fine for a week then this suddenly started happening.
Cartomiser: (carto) Metal tube with polyfil and a coil inside - the kind of thing often used on cigalikes. A tank with a carto(miser) in it is cart tank.
Clearomiser: (clearo) A clear tube with either metal or plastic end caps that holds the liquid which is wicked into the coil. Some look like a "tank" but it is never called that.
Open circuit: The wires don't meet where they should, no current can flow.
Actually most ego batteries that are short circuit protected will flash when they detect a short. I suspect that is what is happening here. Try a different Protank or carto, or replace the head in the one you are using.
BTW, a "short" is a short circuit. We don't normally just say "open" when we mean open circuit however. A short circuit just means that the coil is being bypassed by something and the resistance is not what it should be. The most common reason on a clearo is if there is a bit of wire sticking out the side of the center pin where it enters the grommet on the head. When tight, and especially when you overtighten the wire pokes out further and touches the negative pole, effectively shorting the battery out.