If working manually, it sounds like you have an intensity fader still up at full in another layer. Intensity is defaulted to full at startup on a clean show.
Check your layer-to-mix assignments (next to the intensity fader on each layer on the HUD) and intensity faders on all layers.
Its best to un-assign any un-used layers from mix outputs, if not in use.
Also, if appropriate, you can change the default lib000, file000 from white to black:
- In the Catalyst Menu, go to preferences, application
- from the drop-down menu next to 'Library 0 file 0' select 'force black'
If you later need a white square, its lib000 file 004
Hope it helps, do get back to us if you need more help...
Simon