Nikon D3000 won't hold SD card?

SD card doesn't latch in. The only way the camera recognizes that it's in there's if you manually hold it in, which is difficult when trying to take photographs. This is only a few months old…

Sounds like someone pulled it out and broke the locking mechanism.

Time to send it in for repair.

The camera's age tells me it's still under warranty so Nikon should repair it. You'll have to send it to them. Get in touch with Nikon.