  In this paper, we consider the Langevin equation from an unusual point of
view, that is as an archetype for a dissipative system driven out of
equilibrium by an external excitation. Using path integral method, we compute
exactly the probability density function of the power (averaged over a time
interval of length $\tau$) injected (and dissipated) by the random force into a
Brownian particle driven by a Langevin equation. The resulting distribution, as
well as the associated large deviation function, display strong asymmetry,
whose origin is explained. Connections with the so-called ``Fluctuation
Theorem'' are thereafter discussed. Finally, considering Langevin equations
with a pinning potential, we show that the large deviation function associated
with the injected power is \textit{completely} \textit{insensitive} to the
presence of a potential.
