This is a solution by kkc as posted here on March 21, 2006 - I copy paste the post below:

I could tell you how to edit your saved game file to fix this 03/21/2006, 22:00:29

kkc writes:

Or I could do it for you if you're not willing to try. If you go to the very, very end of any save.HDR file, you can find a string of hex characters which have this value -

3E 000000 B4 000000 B8 000000 C5 000000 C6 000000.

The 3E is a counter and the B4,B8,C5,C6 are artifacts. This string is followed by 58 other values which are all the other artifacts in the game.

Use a real hex editor (not notepad which will destroy your save file) to change the 3E value in that string to 04 and you reset all black chests. It's that simple, just change one byte. The first four artifacts exists in special locations within the game (spencer's, everstryke, black's heart, thjorgard) but if you want them to randomly appear in any black chest, you can change the 3E to 00 instead of 04 and reset those 4 special artifacts as well. Then again, who needs two everstrykes?"

It works wanders and all good again !