Sounds like a hardware problem in which the Superkey doesn't have a good contact with the DS slot. The freezing of games could also be attributed to this, as games will freeze if you eject whatever is in slot-1 while playing.
My suggestion would be to install FlashMe, which will let you boot the Supercard in DS mode without needing the Superkey at all. Do this now, while you can still get into DS mode occasionally. Just make sure you read up on the entire FlashMe process before you do it, as there is some slight risk if you don't take the necessary precautions (insulating the flashing tool). Otherwise, it's a relatively easy and painless process, and will also get rid of the health and safety warning screen, which is a plus.
As kkan said, if you do plan to upgrade to a slot-1 device, avoid anything with the name "R4" in it. There are at least 20 different products with "R4" in the name, and while some of them are alright, many of them are fakes or clones, and getting support would be a nightmare.