I have a Dell E6410 running OS X Mavericks 10.9.3.  I have a 2.66 GHz Intel Core i5 processor with 4GB RAM and NVIDIA video.  Everything has been working great with the laptop over the last few days until I tried to boot without the power adapter. If the power adapter is disconnected, It will boot to the login screen.  Once I enter my password on the boot screen, the screen goes black and I lose video.  I tried booting with safe mode and I was able to login without the power cable so it's some type of video issue.  The strange thing here is that if I boot with the power adapter connected, it works fine.  Any ideas? 
  
Thanks!