I bought a modded GameBoy SP with IPS screen (which looks AMAZING by the way) off Etsy
and surprisingly with some of the old GBA carts I bought off eBay, some of them had trouble booting, I got the garbled Nintendo logo, which is a neat story in itself:
I had to clean the contacts (both cart and GB) with isopropyl alcohol on a Q-Tip and then it was fine. There was visible dirt on the Q-Tip after I did this. I don’t think any amount of blowing would have fixed this one 
