Is this happening with a NuBus video card inserted, or with on-board video, or regardless? Another slot for the video card? Brightness setting and video cable OK? Is the display in use the same one as hitherto? Is the DB-15 to VGA adapter configured correctly? These could explain the lack of video, but the error tones could argue that raster isn't even reached in the startup sequence. VRAM? If you disconnect FDD and HDD in turn, how then?

The car-crash failure sound implies that there is a PPC card in place, so there is another potential villain in the picture unless you meant the 68k Mac rising and falling death-arpeggio.

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