I had similar things happen to my 3ds about a year and a half after CFWing it. It consistently crashed and black screened on startup, and for the longest time I thought it was all software related. I asked several people for help, gave as much info as possible, but it came down to being all hardware related. I eventually took it all apart, up to the touchscreen, then put it back together, and has worked perfectly since. It's a bit tedious and annoying, but if your problem is hardware related, it might work. Only problem is getting a 000 Philips screw. (Got mine at Walmart in a set for like $6)