Store issues

This has happened before, but I am not being able to open the store. I feel bad because I'm missing all the sales and stuff, so if you guys could maybe fix this or tell me what I'm doing wrong, that would help. This isn't the first time my store hasn't worked either. For example, my store didn't work what so ever during the months the snow down skins were available and I couldn't get any, but that's all good. I just want a functioning store back so I can get champions and runes and skins. Please help. Thank you.