After the screen saver starts (set to go on after 1 hour), my MacBook locks up 90% of the time when I attempt to wake it up. I sometimes hit the trackpad and sometimes I hit command. It is hit or miss on which one will work. I have to hold the power button to restart it. I have it plugged in all the time when it's at home. Under energy saver I have both settings set to go asleep after 2.5 hours. I have no issues when I close the lid to put it to sleep. Any ideas on what could be causing the issue?