I've tried almost everything but I just can't select a weapon. The game is unplayable because of it so I'm really upset.. Anyone with a solution?

Don't hold your breath.. A few of us are having the same issue. My weapons are in my inventory but I can not use them, I can't even melee. I have posted on here about it already and so have some others. Hopefully it will be patched but I can not progress any further. Out of interest where did it happen for you, for me it was when I was going to have the memory checked.