software on non-accessible drive

My computer has Windows XP Professional as its operating system. It used to
be part of a network and was set up for that purpose.

I can start up the computer as a non-network user without problems. But
some of the software is installed on a no longer accessible network drive.
Therefore, I seem to be unable to uninstall it.

Worse yet, I don't seem to be able to update or install new software. I can
download the software onto my hard drive. But when I run the installer, I
eventually get an error message 1327 invalid drive, which refers to the no
longer accessible network drive.

The computer is developing more and more problems, but I am unable to
install any diagnostic or corrective tools.

How can I change the settings of my computer to allow me to install new
software on my hard disc instead of the non-accessible network drive and, if
possible, get rid of software whose main part seems to be installed on that
drive?

Thanks for suggestions,

PF