Can you inflate a completely flat tire? I haven't used my bike for almost a year and I need to start riding it again, but it appears I have a flat tire. I don't think there's something wrong with the tube cause I haven't used it for a pretty long time. It just won't inflate. The tire has a  Schrader Valve. I use a pretty old pump so maybe that's the case? I'm not really sure.. So is there any way I could inflate it again without getting a new tube or tire?
You can easily inflate a completely flat tire (provided the tube is still good). Usually, when a tire is completely flat, you have to press the back of the tire so that the valve doesn't recess into the tire so your pump can be attached properly to it. 

With a presta valve, you can use your mouth for this (well, on a clean tube, since the valve stem isn't spring loaded), but with a schrader valve you have to use a pump. 

If it still won't inflate, check the tire and tube for damage and replace accordingly.