i think your machine is fubared anyways, i would suggest a reformat, or do a new windows installation on a seperate partition , just install graphics card driver, and chipset driver for your board, leave away stuff like CCleaner and try a clean poser 8 install there. it sounds like some  optimizer, or similar silly software peoples tend to run these days messed up your file associations, much worse can be the pile of crap building up in your windows system like a patchwork of several incompatible driver modules from previous diver versions which do not get removed, and of course a degenerated windows system, friggen microsoft is the one you should blame here :p  i havent heard of any problems like yours yet, but that does not mean poser 8 is error free, otherwise the service pack wouldnt be released. only problems ive heared so far are crashes on inventory refreshing, firefly render errors, firefly crashes (not new at all) , some even reported issues with newer nvidia drivers.  but a system f***up like yours has the cause somewhere else, you cant test software on the gajillion of possibilities of hardware components you can put a computer together, but you can cover the most common configuration of components and operating systems, and then there are still those with odd combinations of components which wont work together under given situations, i have built a machine like that once and was ending up getting a different motherboard because of quite unexpected incompatibilities with my graphics card manufacturer, different brand of the same card i borrowed from a friend worked, but i wasnt willing to shelve out 400$ more, so i bought a different motherboard, and the friggen thing worked flawlessly.  sometimes such issues do not show up until something happens like in your case.

so if it is not a messed up windows installation, not the driversm then you have the odd and rare case of "my systems components just do not want to work together with poser 8, just because" gremlins

yeah...and try to defragment your drives <_<