Computer memory card not reading....... help please?

You say when you put the card in, it fits. Why did you take it out? Is it a new card? Did you make sure it is the proper card for your computer (make, model, max RAM)? Once again, why three different cards? If you have a Staples Office Supply where you live, take the cards to the Technical Support desk, along with the info for your computer and ask them for help. That is what I did and my computer is running not only fine, but faster (increased the RAM with a new card).