Switching capacitors in a guitar effects pedal
First a schematic diagram rather than pictorial.



This is a very basic single amplifier stage with a voltage gain of approx R3/R4. 

Its more of a bass cut than a treble boost (you're cutting out the bass notes) so you lose the bass below the cut off frequency allowing more of the treble to come through. 

C3 and R1//R2 form a high pass filter (CR). With C3 = 100nF the sound is OK. 

When you switch in the 10nF your are raising the lower cut off by a factor of 10 and the 2n2 by a factor of 45 (ish). 



Let's assume that the 100nF gives a lower cut off of 500Hz. Then 10nF gives a cut off of 5kHz and the 2n2 gives about 22.5kHz (i.e. above the threshold of human hearing). Little wonder you can hardly hear anything.

A further complication is the value of C2. If this is too low it also acts as a high pass filter.

Some possible solutions:

(1) Make sure C2 large enough to give a full frequency range output and not acting as a second high pass filter.

(2) Choose values for C3 in a much closer range (2:1). Try a slightly larger value than 100nF as well (say 220nF (more bass), 100nF (clean) and 47nF (trebely))