Hi dusan, Was there any type of overclocking that you are aware of? If so try setting the clock levels to normal speeds.
Please check to ensure your power supply is plugged in all the way before proceeding to the next steps. If the power supply is plugged in all the way you can try using a known good power supply if possible. If you do not have an extra one you can always ask a friend or a nearby computer shop to test the power supply with a known good one. If it's not the power supply, please view the next step.
Please run a hardware diagnostics using HP hardware diagnostics to help you determine the cause if your able to boot into windows at any point. If not you may need to test the physical hardware using the old fashion method since your having problems with the BIOS.
The CMOS battery could be to blame. Have you tried testing the hardware components to ensure that the CMOS battery and other components work? You can try testing a new or known good CMOS battery in your system to see if that works.
If you already tried the troubleshooting step above and it's not your CMOS battery it is possible that a key on the keyboard could be stuck or your backlight key may be turned off or faulty.
Your graphics card, CPU, video adapter or even the hard drive could be failing.
