You can install PSpice for TI and other Cadence Allegro products on the same computer, as long as they are all installed into separate directories.
If you have multiple Allegro products, you might have used the switch release utility to set the proper path before running each of them. PSpice for TI does not interfere with those products, nor does it use those settings.
If you think there's something not running right with your Allegro products that are installed on the same machine as PSpice for TI, please use the switch release tool provided with those products to check if the correct product/version is selected.
In SPB 17.4, Switch Release can be found:
Run Switch Release to select the version you want to use, and click OK, then launch the tool:
If you don't see Switch Release in the start menu, it can be found as <install_dir>\tools\bin\switchversion.exe.