IT never goes over well when you pass the blame for a failure back to the user. Sorry about that.
Some things to watch out for is to NEVER over tighten a carto onto an eGo. NEVER. Once, and it's over. Expecially it the outer shell contact of the carto is a little long or the end is a little damaged. Cartos damage eGos more than any other cause.
I also hate hearing about the IGNORANT recommendation to pry up the center pin on an eGo.
The pin is designed to not rotate in the insulator, to keep from twisting the little wire going from the pin to the circuit board inside. It also has a flange on top to PRESS AGAINST the insulator. If you pry it up the carto will just push it down and turn it in the process. The raised pin will not put enough pressure against the carto center pin to make a good electrical connection. A lifted pin may actually SHORT OUT against the shell of the carto, killing your eGo in the process. Prying it up also sets you up for juice leakage into the eGo circuitry. It's not so much the juice, but the hygroscopic nature of PG/VG that absorbs water from the air causing internal connections to corrode. Play with the center pin of the carto if you must.
Troubleshooting eGO FAILURES via the internet makes for an interesting read. Some of the "5 click ON/OFF" suggestions are a waste of good bandwidth

If it's flashing at you, it's ON. If it starts flashing with a carto on before you even press the button, it has a shorted Mosfet, and will not work. Oh, and the eGo will never know it has an OPEN carto on it.
If all the above was too complicated just remember,
don't eff with the eGo center pin,
don't over tighten a carto, not even once,
funny flashing means something is wrong.
EDIT:
Most eGo users don't seem to either have a voltmeter, or really care to troubleshoot electrical problems with one. Fine, it's complicated

How about a cheap one dollar 3 ohm carto, or a 4 dollar 2.5 ohm atty? Don't like vaping those? Fine, keep it for troubleshooting. 2.5 to 3 ohms is a safe way to troubleshoot. Lightly screw it in until it makes connection and see it the eGo 'Likes' it. Now, if your eGo doesn't 'Like' your fancy dancy tank, it's probably not the eGo that is at fault.
People have learned not to get caught with only one battery or only one tank, but what about one $3 charger?