What did it say before? Also, did you make sure to replace the coil if you took it out for cleaning (sorry, just gotta ask) and make sure it was screwed in tight but finger tight? Are you using a new coil?
Also, it could be either the tank or the mod, or user error, really. Sometimes, gunk can build up in the 510 connection of the mod, and sometimes a tank will get stripped or otherwise not connect well to the mod.
If this is a friend, enlist his help. If this is a "friend" well, it's possible you were sold a faulty device. Do look at the tank pin, does it look stripped or otherwise damaged? You can try "gently" prying at the 510 connection to see if it's stuck. Do NOT use extreme force.
The easiest way to isolate the problem would be by trying the tank on different mods, or a different mod for the tank. I really can't say if it's one, both, or neither. Normally I'd suggest a vape shop to assist you in person, but it sounds like you may not have access to one.... If your pal is truly a pal though, perhaps he can help you figure out the equipment.
Hopefully someone will be along with more suggestions than I have. Best of luck and welcome.
Anna