Lefu

A few months back, i bought an older game that had problem recognizing more than 3GB of RAM, so I turned the RAM down to 3GB is msconfig. After beating it, I uninstalled it, and I thought I had changed my RAM back, well a few months later, I checked and realized that it was still 3GB. I tried to change it back to 4, but it was basically saying the max was set at 3, despite having 4. How do I fix this?