Im having some trouble here, please help!

DanLights

Santa Hat Forever
Im trying to record a guitar but volume is coming too low showed in the peaks of the Reaper. In the VU meter of the track is looks it´s coming in at OK level, but when I record the peaks in the multitrack it´s almost mute. Im using this:

LTD Explorer with Emgs (81 and 60)>>Electroharmonix Metal Muff>>Peavy Valve King head>>Peavy XXX cab>>SM57>>Lexicon Alpha>>Pc with windows Xp>>Reaper

I tried the bass yesterday and it came it perfect, with this signal chain:
Ibanez Gsr100>>Zoom 506II>>Lexicon Alpha>>Reaper

please, any ideas why the guitar sound is being recorded too low?