R4 stopped working without help

[Kronikarz]

My R4DS stopped working recently, I thought it might be something with the card not connecting properly, so I inserted my fingernail between the card and the back of the DS, near the SD card slot, and it booted OK. When I remove my fingernail it usually continues to work, but when I move the DS sharply it stops. Also, most recently the R4 rarely boots up even with my fingernail in the slot. I tried putting some paper there, but it almost never works.

Any ideas why and how to make it work again?