Have you tried loading and manipulating it with HW Shading off? Does the problem happen when you switch to SReeD?

Another thing which you should always do when things like these happen is to reboot the machine - this will also reset the hardware (videocard)

Something must have changed since it did work previously. Big problem is always to find what has changed. Deleting poser.ini resets everything in Poser to default state and this will help if the preferences have somehow corrupted.

Other possible causes are

 - a Windows Update which installed another video driver

 - a new texture/node setup which causes the problem (but you said you already tried the original model with its original textures)

 - Did you turn on multpi-threaded bending? (deleting poser.ini should have turned it off again)

Of course there is always the off chance that you have a hardware failure, but I don't think that is the case.