The System has not been modified?
That sounds like something you would see on an incomplete setup, or a program that can't be installed...
You know, the "The installation could not be completed. The system has not been modified. You can run setup again later"...bla, bla,bla stuff...
One question: Do you get this error while trying to install some Nvidia drivers or when trying to install Itunes? I've seen it on those setups...
If so, then check if:
1. You have system minimum requirements to install the program.
2. You have full access, privileges or are an administrator.(Regedit)
3. You may have a service stopped. (start>run. Type services.msc)
More details!