You just need to create some logic to get your work done. Here people will not gives you all code but here i am giving you one of the sample how you can do that,
private bool checkDiagonal()
int i, j;
for (i = 0, j = 4; i < 5; i++, j--)
if (abc[i, j] != true)
Hope you can generate similar function for others. you can even use Modulus operator
for other rows and columns value matching in LINQ function.
Best of luck