Few days ago I installed a brand new Ubuntu 12.04 on my Dell Latitude D630 machine. Everything seems to work fine but problem is with shutdown/poweroff. My machine won't power off correctly. After starting shutdown procedure Ubuntu shuts down, OS turns off, but machine won't completely power off! Screen is black but green power led is still on and ventilator works (probably like CPU, MEM and HDD) in background! How to solve this issue?