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I had the same problem, but I played the game on Linux. My solution was to add the game to Steam and launch it with the Proton Experimental compatibility layer. This worked for me.

In the Ice Cave, you have to find 4 switches in one corner of the cave. 2 of the 4 switches must be turned on. If you have turned on the 2 correct switches, you will see an exclamation mark symbol above the player. After that, the crystal can be reactivated.

My inspiration was the Vampire's Dawn II KS Demo.