|Perform the following steps:|
1) Restart the computer. Immediately after the screen goes black for the first time, press the F8 key repeatedly. Advanced Options window appears. If the menu does not appear, restart your computer and try again. Use the arrow keys on your keyboard (the mouse does not work) to select Last Known Good Configuration, then press ENTER.
2) If you have recently installed new hardware, turn off the computer and disconnect the hardware.
3) Restart the computer and press F8 again. This time select Safe Mode and press ENTER