1995 Pontiac Grand Am Power Steering

Over the past two winters, my car will lose power steering when I attempt to start it after particularly cold days (under 40 degrees F). When temperatures rise above that, the power steering will return. While this has been problematic, I haven't bothered getting it fixed, opting instead for waiting on higher temperatures. More recently, it has stopped working in warmer temperatures. The steering fluid level looks optimal. What else can I look for!