Do I have a defective Nikon D5100, or is it just my memory card?

I recently got this Nikon D5100 for my birthday. I have been using a SanDisk 4GB and sometimes a 2GB card, you know the little blue ones(I plan on purchasing the correct type). When I first got the camera it let me go up to 1/4000th of a second in shutter speed. Now it doesn't let me go past 1/200th of a second. I also noticed recently when I first tried out continuous shooting it wouldn't let me. I reset the settings and it still hasn't been working. Any Ideas as to what's going on?

Added (1). Thank you! And yeah, I'm new to photography and I'm starting a class in a couple of weeks.

You need to take some time and read your user manual.

When using flash, the fastest shutter speed you can use is 1/200th second

A memory card needs to be formatted before use and again after you have safely copied all the images from it to your computer at the end of each day, but has NO effect on the cameras shutter speed performance.

Continuous shooting must be done with the cameras shutter speed set to higher shutter speeds.

You neglected to tell us what shooting mode you are in. The manual mode using the light meter to determine the shutter and aperture settings will for sure allow you to shoot at 1/4000th second outdoors.

It seems that you need to learn more skills using a fully adjustable camera.

A nice class in beginning photography is recommended