Thanks for advice with tags for code.

PS. In main(), you're recursively calling main(). This is not allowed. main() can't call main(). Use a loop instead.

this should work.
Code:
int main() {

	char choice = 'n';
	do  {
		gameMode();
		resetBoard();
		cout << "Velaties spelet vel? (y/n)";
		cin >> choice;
		system("CLS");

	} while (choice == 'Y' || choice == 'y');
}

i think this is problem. At start array board[9] were empty. And then i added numbers for easy play. No 0 and 1 typing etc.