Assuming that you are using the supplied libraries from the installation, I suspect that there is no global reference to "nom.lib" - set this up through the following menu options, PSpice>Edit Simulation Profile, Configuration Files tab, set the left had selection to "library", use the upper Browse button to browse to "nom.lib", in the product installation directory, then "tools\pspice\library", having selected the library, use the "Add to Global" button to add the library. Also, check that the path next to the lower Browse button references the "PSpice library" directory mentioned. OK to close the Simulation Profile dialog.
(If you don't have an existing Simulation Profile, create a new profile and the libarry settings to that. "Global" will apply to "all" simulation profiles designs)
The setting for the "nom.lib" reference should have been configured during installation so "something else" may be wrong with the installation.