Upgraded to 5.1.0.29 and now receiving a dos box:. "c\windows\system32\cmd.exe"

Norton 360 did an update to 5.1.0.29.  Since then, my pc has been running extremely slow and every time I start my machine, I get a dos box that doesn't go away.  The box is titled "c:\windows\system32\cmd.exe."  How do I get rid of the box and how do I get my machine to work faster again.