  We present a multi-mission X-ray analysis of a bright (peak observed 0.3-10
keV luminosity of ~ 6x10^{40} erg s^{-1}), but relatively highly absorbed ULX
in the edge-on spiral galaxy NGC 5907. The ULX is spectrally hard in X-rays
(Gamma ~ 1.2-1.7, when fitted with an absorbed power-law), and has a
previously-reported hard spectral break consistent with it being in the
ultraluminous accretion state. It is also relatively highly absorbed for a ULX,
with a column of ~ 0.4-0.9x10^{22} atom cm^{-2} in addition to the
line-of-sight column in our Galaxy. Although its X-ray spectra are well
represented by accretion disc models, its variability characteristics argue
against this interpretation. The ULX spectra instead appear dominated by a
cool, optically-thick Comptonising corona. We discuss how the measured 9 per
cent rms variability and a hardening of the spectrum as its flux diminishes
might be reconciled with the effects of a very massive, radiatively-driven
wind, and subtle changes in the corona respectively. We speculate that the cool
disc-like spectral component thought to be produced by the wind in other ULXs
may be missing from the observed spectrum due to a combination of a low
temperature (~ 0.1 keV), and the high column to the ULX. We find no evidence,
other than its extreme X-ray luminosity, for the presence of an intermediate
mass black hole (~ 10^2 - 10^4 Msun) in this object. Rather, the observations
can be consistently explained by a massive (greater than ~ 20 Msun) stellar
remnant black hole in a super-Eddington accretion state.
