I killed Rashgar, kept his head, went to see the ghost of the king on the level 1a of the orc caves and then came back to Hillbrandt. I talked to the sheriff and first gave him all my orc heads and scalps and now there's only Rashgar's head left in my inventory and for some reason the sheriff doesn't react at all? If I want to talk to him it just shows "That's all for now, farewell", showing that I already talked about everything I could with him and there's still the "I want my reward for the orcs killed" text but when I chose this option it just shows the "That's all, farewell"...

Is it a bug? Or maybe I was supposed to give the head to the sheriff and then complete the quest with the king ghost?

I just realised my stupidity, I was supposed to give the head to the Duke and not to the sheriff...

Use ` (backtick, left of 1 on QWERTY) and type:

\givenewitem HlavaRashgar

That second letter is a lower-case L.

I know this is an old thread and it won't help the OP, but I had the same problem and this is one of the top search results, so maybe it will help someone else.