MXL 991 + TASCAM 144 "Hiss/White Noise"

Hi y'all,

I am brand new to home recording music, and I just received an MXL 990 mic, a 991 mic, and a Tascam 144 mkII USB interface with 2 audio cables.

I plugged in the 991 to record some acoustic guitar in garage band, and I get a constant white noise/hissing sound as soon as I begin to record. For the "input knobs" I have a choice of turning the knob down (says "line") or up, (says "mic"). The white noise is reduced if I have the knob turned all the way down, but not eliminated, and the mic does not pick up the guitar very well. If I turn the knob all the way up, it picks up the guitar, and a ton of white noise.
I have tried...
- mic closer and mic further, (2in to 12 in, no difference in hiss)
- using the other input, no difference
- using the 990 mic, still no difference
- moving the mic like 15 feet away from my laptop

My room is not huge and echoey, nor is it all that loud. I know I am bound to get some background noise, but this almost drowns out the guitar.

I would love, love some help.

Thanks!!
-Will