sounds like the upper lcd ribbon was torn during installation. if you're lucky, it's simply not inserted to the PCB connector properly. but since you already rechecked the connection, it's probably the former. good luck.
if you have a microscope, you can solder a 32ish AWG wire from the charge port or whatever to the broken trace. just scrape the coating from the broken trace with an exacto knife. again, not easy without a scope, but pretty much the only way to repair a damaged pcb trace.
either: 1) the pins that make contact with the game are bent/broken/dirty. look into the reader with a flashlight and see if anything's going on. rubbing alcohol + small brush will take care of dirt. tweezers can take care of a bend. broken pins will require a new reader to be soldered in 2) bad solder joint between the reader and the main PCB. Reflowing is a pretty easy job if you have the tools, a replacement is a little more complicated. good luck
The top LCD is not a great DIY project unless you're used to handling small ribbon cables. If you aren't careful, you'll tear the new ribbon as you're installing it. New LCDs are $10-$20 on ebay. Good luck.
2 possibilities. 1) the pins in the card reader that make contact with the game's contacts are bent or dirty. look in there with a flashlight and see if anything's going on. if it's dirty, try using a small brush + some isopropyl alcohol. get in there with a tweezers and try to reshape the pins if you see something bent 2) bad solder connection from the reader to the main PCB. will need to be resoldered. good luck.
I don't think this is related to a fuse. It sounds more like your connection is loose or dirty. I'd suggest cleaning the charge port on the DSI with a small brush + isopropyl alcohol. If it's still doing the same thing, you probably have a bad solder connection on the charge port. A bad charger is also a possibility.
I had the exact same problem. It was my first attempt at a repair, so I did a ton of work that was not necessary. Long story short, it was a simple fix. The small wifi sub-board went bad. swapped it with another and all the symptoms went away. Again, the exact same problem as you - camera works, can't load any application (system settings, insert game, pictochat) or the same error you posted occurs. If that wasn't the problem, I'd be surprised.