Cannot go to BIOS in M4800

Hi All:

I cannot goto BIOS or one time Boot options screans by pressing F2 & F12.

I did not make BIOS update, I noticed this happened suddenly, and my M4800 was working normally. When I press F2 or F12, I am getting a blank screen.

I tried every method mentioned in the following documents:

https://www.dell.com/support/article/us/en/19/sln151669/using-the-advanced-startup-options-in-windows-8-on-a-dell-pc?lang=en

https://www.dell.com/support/article/us/en/19/sln143038/access-uefi-bios-system-setup-from-windows-on-your-dell-system?lang=en

with no hope. Only one thing let me goto BIOS setting screen sccessfully. I turn off the laptop, remove the coin battrey connector for few minutes. This let me go to the seeting screen once ONLY. If I make another restart and try to go to BIOS setting again the problem return again, where a black screen is shown.

When I press the F2 key, the blue loading meter indicating that I am going to the BIOS setting, but after that I got a blanck screen.

Windows works normally without any issue, and there is no delay in time so that I can expect the battery voltage is low. I bought this PC since 2014 and I use it since then every day.

Thanks for every suggestion