9800 doesn't recognize a newly filled cartridge

[Dag57]

I’m new to the game and my 9800 didn’t want to accept the first cartridge. After re-inserting the old one it suddenly took it. i’m not sure what I did to make it work but now on my second one it won’t either. I’m trying things but it seems silly not to work, do I have to reset a new cartridge if never used? I did that too thinking that was the problem but not so sure.
Ok, I think the problem was not pushing the cartridge in firmly enough. It seems to be working now. Thanks.