Keys are not IP specific. You may want to right click on All Keys in the PGP module on the left hand side of PGP Desktop, select Properties, and make sure the correct keyrings are set. You may then check your key listing in My Private Keys to make sure your key is there. If it is, right click on it, select Properties, and make sure Trust is set as Implicit.
If this doesn't do it, either set your keyrings to whatever location you have for other keyrings that may contain the necessary private key. Or going back to All Keys, you can use the File menu to select Import to import from other private keyrings, but any imported private keys will need to have Trust set to Implicit (as above).
If none of this helps, please state how you are trying to Import the private key, and what actually happens.