First, you will want to verify that the 4 cans you installed isn't too much, or that its enough. There should be a sticker under the hood to let you know how much the system holds. Also, was the system empty when you charged it? Did you fully evacuate and pull a vacuum on the system? Air in the system and/or incorrect system charge can make these finicky systems act funny.
If all is well, the system may just need reset. If a problem is detected, it shuts the system off to protect itself. It has no reason to believe that the problem was fixed since last key cycle, so it requires an actual reset. This can often times be achieved by disconnecting the battery for 30 minutes.
The next step would be to install a set of A/C pressure gauges so the high side and low side pressures can be observed. You could have a failing compressor or restricted orifice tube, both diagnosable with pressure gauges.