Can a virus “block” the monitor (it doesn’t show anything, not even BIOS POST messages), or is it always hardware prblem?
My guess would go to a Hardware issue, I think if it would interfere with BIOS POST messages it needs to have infected the BIOS.
Does the system ‘beep’ during startup, normally hardware issues have specific number and sequence of beeps to indicate hardware related issues.
No beeps, monitor light is blinking, monitor and wire tested on other pc - works fine, integrated video card.
Well unless you have a strong feeling it could be caused by malware my guess would be hardware failure.
Did your system act strange lately? any clue of infection like behavior?
Yes, computer is infected with winlocker type virus and we’re trying to figure out is it virus that causing black screen or is it hardware issue. I never encountered a virus (trojan, rootkit or winlocker) that is able to do this.
I don’t think that I have heard of an infection that can prevent the BIOS boot message from appearing on the screen before. What’s the make, type and age of your motherboard?
Winlocker is FakeAV with only one goal, make money, they won’t blank your screen they will make sure you can read the ‘Put the money here’ message…
Can you put a PCI video adapter in the system see if that works?
Hi Maniak2000,
Well, as Ronny said, it is most likely a hardware problem, but…
True again!
I was surprised by
Yes it can, Kail. You can find tones of info re: the matter 
At the same time, old BIOS (especially if you never taking care of updating /upgrading it) can be just corrupted, without any malware involvement
Combining 2 related messages:
Good point by Ronny re: the adapter! Connecting your monitor to another PC cannot be considered as a complete test. Changing the adapter(s) here - alleged infected PC, and there – the clean one can shed some light on.
Finally, re: “Winlocker is FakeAV with only one goal, make money…” Sure that is true! … but in ideal gas (I mean world 
) environment.
Most current malware are “non-destructive” & the aim you’ve pointed is correct (including Fake AV). From that perspective – indeed what would be the point? PC must work perfectly.
But we should not forget that may of those malwares have been modified very frequently and
the old strains (modified as well) are still being “available”. Most of the security are failing to identify them anyway. That’s where, in simple words - being “non-destructive” basically doesn’t matter for some malware devs and indeed most of those “fake AV’s”, alike & others will bring Rootkits/ destructive nasties, etc.
Unfortunately at this point there is no certain answer to OP … unless it’s 100% proven that the cause is not an old graphics card failure/ BIOS being corrupted (or maliciously re-flashed)
Those two mentioned as a matter of fact can be cured, by PC manufacturer (please visit their site)
Cheers!
Sorry for keeping quiet, you see the problem is with my friend’s work PC, and he said that it will be very problematic to change hardware in that thing… and I can’t contact him at the moment, so no new info from there.
Here’s what I know of the problem.
A few days ago my friend called and said there is a virus on his work pc, it was a full screen message about visiting xxx sites and that he must pay to unlock windows (typical winlocker), it also said that in 12 hours all data will be lost (I thought it was also a fake warning…now i start to doubt that).
Keyboard shortcuts didn’t work (i.e Ctrl+alt+del) and safe mode was inacessable.
I said that we need boot cd \ usb to fix that, wich he didn’t have, so he turned PC off.
Later that day (by evening) I made him a bootable Cd and next day when he got to work there was current problem.
I’ll write more if I will be able to contact him.
Even though making changes to hardware may not be wanted very much it is best to persuade your friend or his employer to slot in a PCI graphics adapter. When that works see from there. When you are familiar with flashing a BIOS I would recommend that.
Coming from the hardware angle also consider an old and failing BIOS battery.
Well it turned out that the integrated video card died… so it wasn’t actual virus’ fault.
It was suspected as much
Thanks for letting us know
Were they able to change the card or
disable it trough BIOS & add a new external one or
whole motherboard had to be replaced?
Cheers!
Unfortunantly he wasn’t there when that PC was fixed, so he only told what was wrong with that black screen (someone must’ve told him).