I signed up to this site just because I didn't know anywhere else I could get help with this

Anyway, I've had an Action Replay DSi for about 5 or 6 years, and after not using it since about 2012 I picked it up again because I wanted to use a code I found just to change my Wild World character's face, but my Action Replay refuses to work now
It works fine with New Super Mario Brothers, but not with either of the two Wild World cards I have... I press boot and it just stays on the black screen, doesn't even get as far as the Nintendo logo
For some stupid reason I thought deleting all my codes would work (spoiler: it didn't, but I never used any of the other codes anyway) and any methods of resetting the AR I've found online don't work (like the a+b and start+select ones.. I lost the cable and the CD yonks ago)

Animal Crossing Wild World worked 100% fine when I first got the AR, and since it still works with other games I'm not sure the exact problem. It's a European AR and both the cards are European, the.. version?? code?? thing on the back of the two cards is ADMPNOJO9 and ADMPNOJO8. Not sure if those are meant to be O's or 0's

Also the two cards work fine without the AR so I know it's not bricked. It's also not a case of there being too many codes, since at the moment I only have the master code in, and before that it was just the master code and about 4 other codes, 2 of which weren't in use.

Any help would be greatly appreciated! Any forums I've found with problems similar to this were from about 2008 so I'd be delighted if there's still help around