What are you recording ? If it's your voice through a mic, what kind of mic is it ? If it's a condenser mic (like an AudioTechnica AT2020), you need phantom power which you activate by pressing the 48v buttton, and then turn the preamp gain up on the input you're using, until you can see the signal coming in (you should see the level on the unit itself).
If it's a dynamic mic (like Shure SM58), you don't need phantom power and so your problem is elsewhere.
Certain kinds of mics can be damaged by phantom power (like ribbon mics), but as you sound like you're starting out, it's unlikely that you have one of those. If you're uncertain, you can google what kind of mic it is or post it here.