Error on loading os

When I start the pc (hp pavilion 4550z) it gives a message about an “unistallation of a SW incomplete and tell that could’n find “ndisman.vdx”, press any key.
After that it, when the icons appear it says:
“unastallation error”
unable to open the installation log registry key noshow. installation will not continue.
I cancel this message ans the system goes up.
It seems that somebody tried to unistall a program without success. how can I find out what is the cause and correct it.