Notebook won't start, it shows nothing but a black screen.

[VeseliD]

Hello,

I have problem with ProBook 6555b: It won't start at all.

Everytime, when I push the power button, it shows nothing at all but a black screen. No HP screen, no beeping sounds, no LED blinking or something else. Anyway, sometimes I'm succesful with powering it on, but it's like on 50th try. When I'm succesful with booting it, sometimes it shows "CMOS checksum is invalid" - CMOS reset 502. Then, the system will boot up, and works perfectly fine, until I shut it down again. It also displays wrond date and time; it's allways the time since the last shutdown.

Today, I've tried the 'Start Up test' which is in the BIOS setting, it got stuck at 84% on "Optimised DST check". I've also realized, that when it won't boot, the HDD LED lights orange color. When it's succesful, it shows no light at all, sometimes a blue light blinks. I've also tried to reinsert RAM memory or BIOS reset, which is written in the support as a advise. It has no effect.

Does anyone have any advice, how to solve this problem? Thank you for any reply.

[PiterGeek]

Have you tried power resetting your laptop? If not, please follow the guides below and see if the process helps. 

https://support.hp.com/in-en/document/c01684768

Or alternatively you can try to restore the BIOS.

https://support.hp.com/us-en/document/c04126730

[VeseliD]

I've tried both of your advice before, and unfortunately, none of them helped.

[PiterGeek]

You may check out both the power supply and battery. Or test it with a different HDD and RAM to see if the fault is from the Motherboard.