First off, when you reinstall, did you completely remove all files, including those in My Games?  That may or may not be relevant but it doesn't hurt to check...

Another thing that may be an issue...run steam as an administrator, and install Sins that way...probably won't make any difference but it never hurts to try...

Now, to the real important stuff...did you have a change to your video card driver?  Did you change your OS?  Do you have faulty sectors on your hard drive?

looks good now. thanks Seleuceia. I uninstalled everything clean meaning deleting all my files including the ones on my saved game multiplayer recorded game files. It's like a fresh start so that means I had to delete my old recorded game files . I don't think that was the problem. I saw some steam and sins crash report stored away under my steam file somewhere unusual spot and also deleted those. I found them after I uninstalled sins rebellion. Figured that may as well delete everything about rebellion and start off fresh.

LoL! I was almost defeated because the crash file or bug report had z axis its way from my sight unto another part of folder and I had to locate it else where by using my own z axis movement.