Windows is set to display a res or refresh rate your monitor can't handle.
Boot into Safe Mode and drop the res there. Reboot and it should be fine.
I just installed the Radeon 9550. When my PC boots up and goes to the log-in screen it's fine, but when I log in the screen goes black. Something to do with the refresh rate? Any ideas?
I had to disable the card and went to using the PC's original stuff.
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