continuing off the tangent, "party" is a noun, not an adjective. In a construction "party politics", it functions _like_ an adjective, but it remains a noun.
Similarly, "computer" in "computer games" is a noun that modifies the meaning of the following noun. Modifying nouns like this always are in singular.
Similarly, "computer" in "computer games" is a noun that modifies the meaning of the following noun. Modifying nouns like this always are in singular.