Hello,
Hard to guess with what information you provided. Boot up off of a CD-ROM, but do not do any installs or maintenance. Just have it sit at the Welcome! screen for a while. If it maintains the bright clear picture, then you have a software problem with the OS X installation on your hard drive. If the monitor is dim, and you see no changes, I would argue a hardware problem.
By the way. Mac is not MAC. We are not an acronym. Mac.
Christian
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Posting Virtuoso
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