Shutter Speed / Aperture Query - stuck on "LO"

[BobbyFowler]

I've got a Nikon D90. I'm trying out the 2 modes, "A" & "S". I'm looking at user videos on youtube. On youtube as the guy increases or decreases one of the two, the other increases or decreases accordingly. On mine, if I'm on "S" , the aperture is "LO" and doesn't change no matter how high or how low I go. The same thing when I'm on "A", the shutter speed is stuck on "LO". Anyone know if there's something I'm not doing correctly?

 

[vandriver]

I own Canon equipment myself,but just a few basic questions:
What lens are you using,and under what lighting conditions are you performing your tests?
What ISO setting are you on?
Lastly(apologies for this one) Do you have the lens cap off!