Q: Can I play my old games on my 2DS or 3DS?
Simple answer is yes. All the 2DS does simply is to remove the option of 3DS away from the player. All DS games will play in this console, this means its backwards compatible allowing you to play all DS games but not forwards compatible, this simple means that you can not play 3DS game cartridge in anything other than 2DS or 3DS.
On the DS consoles they can Play all Pal & Eur Regions providing your console was purchased from UK or Europe
Q: Why is my DS saying Game not inserted?
Well this is simply because over the generations of Nintendo consoles this has been a flaw of them! The simple way to rectify this to blow into the game slot where you insert the games and across the game cart where this board is on the back of the cartridge.