Laptop doesn't boot or enter BIOS or show anything

Hello,

I have a 6 year old Toshiba Satellite C660 2QX. The problem I am experiencing is that when I turn it on, nothing happens. More specifically: the screen turns on, but nothing is displayed. I know it's not the Ram sticks, because I tried that already. The splash screen isn't displayed and I can't access the BIOS. I tried holding F2 or F12 pressed before pressing the power button. It worked, but briefly. I wasn't able to do it a second time and when I did it the first time, the BIOS exited after about 5 seconds. I tried reseting the CMOS. That didn't work either. When the laptop is turned on, it acts like it's stuck at splash screen level and not going forward, because I don't have to hold the power button to turn it of, just press it. Also after removing the HDD, it gives me the insert boot device message, without passing through the splash screen first.
PS: I didn't activate the fast boot option.

Can you please advise me what else to try, or propose a diagnostic?

Thanks!