I can't sing low note! Help!?

Whenever I sing low notes in a song, my singing seem like those that don't have tune/melody (Like talking). But whenever I sing high notes in the same song,my singing have melody and is smooth.

I felt really uncomfortable hitting low notes,my voice always seem weird and I'm more comfortable hitting high notes.

Is there any practice I can work on for singing low notes?

P.S. I have another question,sometime I sing like I'm talking at some point,is there a way of practice to make it better? Does this mean that I can't sing?...