The V4 will on power on do a selftest.
During the selftest, hardware and memory are tested.
The screen will change colors during different section of the test
Please read here for more detailed informations
Do you see the colors change on selftest?
If not, next question is, did you see them before.
The selftest goes rather quick... and some monitors are little slow on syncing and might not show it fully as they are still not synced.
If you see the selftest but later only black screen when the OS did boot up,
this could be something harmless, like selected a Screenmode in the prefs that is out of the range of your monitor.
Can you enter AMIGA EARLY BOOT MENU ?
(you go there by holding both mouse buttons pressed during power on)
Or can you remove the CF card, (just pull out) you should then "Please insert Disk Screen"
Does your monitor shown them?
Which OS do you use currently? You said Vampire 4 OS, did you mean "Apollo OS"?
Which version of it are you using?
In my experience is pretty easy to on Amiga to select a screenmode outside of the supported range of your monitor. If this happened you will see no screen after booting.
You should see the selftest color change, and you should be able to enter Early BootMenu, and you should be able to select to boot in CLI, from which you can set the Screenmode setting back.