Hi ngocn,

Welcome to the Community.

On the Dell logo tap F12 key to open One Time Boot Menu. Select Diagnostics to perform ePSA Pre-boot System Assessment. It will check all the components of the system and provide you error code if any.

If the diagnostics pass, restart the system and tap F8 on Dell logo for Advance Boot Options. Select Safe Mode and hit enter.

Let me know if the system boots to safe mode or provide any error code during diagnostics.

Also, let me know the operating system installed on the system.

Thanks & Regards
Manshu S
#iworkfordell

I have the same problem, but on a Dell Inspiron 7720 17R SE, on Windows 8, and using F8 does not bring up anything.

Using F2 to go to the BIOS, I cannot find any "Safe Mode" option.

I have exactly the same problem on an Inspiron N7110 R17 laptop running windows 7.  It was just fine this morning, but this evening, the screen goes dark with a blinking under score after the Dell splash screen.  And, I see nothing when pressing F8.  But, I can get into F12 and F2, so it does not seem to be a problem with the Monitor/screen/panel or the video card.  It is something else.  But what?  

I really need help on this.

Hi ngocn,

Please refer to Dell Article 584333 using the link mentioned below:

http://dell.to/13VnxCM

Thanks & Regards
Manshu S
#iworkfordell