At times the "failed to build a preview graph" error measage appears when the editor has a problem with the capture file format. By STUIO 8 I presume you mean PINNACLE STUDIO 8? Try changing your capture settings, like MPEG to AVI or vice versa.
Otherwise download the latest patch for Studio 8 from www.pinnaclesys.com
. It's free if you have registered your copy of the software.
Let's hear from you again. All the best.