Sony Projection TV - from light to dark

I have Sony projection tv that has been moved three times. The first
time is was moved a color gun went out. It was under an extended
warranty at that time and was replaced and worked perfectly after
that. One year ago I moved again. A month or two after moving the
set began to go from an excellent picture to a very dark picture. The
color does not change but everything becomes much darker. I have
changed all settings to the brightest and sharpest. I don't know if
this is something a layman can fix or if I have to have a professional
do the work. I would appreciate any incite someone could give. Thank
you in advance.
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