I would say:

• either the Library startup is not finished yet or won't finish at all (it should leave a second icon on the taskbar, bring it upfront and watch the counter at the bottom)
• or Poser itself has a sudden problem opening the user interface, which usually is OpenGL / video-driver related.

"without reason suddenly" is not a habit for computers. Did Windows Update installed a new videodriver perhaps? Open Windows Update and look at the history.

Re-installing the Poser software, perhaps? Perhaps something "improved" on the registry.

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Usually I'm wrong. But to be effective and efficient, I don't need to be correct or accurate.

visit www.aRtBeeWeb.nl (works) or Missing Manuals (tutorials & reviews) - both need an update though