Tools not working

So ive been using aseprite for a while now, but ive had this problem where sometimes the tools stop working. i go to a normal layer, and when i use the brush, eraser or any other similar tool, it shows the little cursor with the anti symbol next to it, which is only supposed to help when the layer is locked. it wont let me draw at all. additionally, when i use the select tool, it looks like its working, but then i use command + c, and then command + v, and it just doesnt paste anything. this only stops when i save and close the sprite im working on, but lately its been starting again almost instantly after i open the sprite again. im not sure what to do. im on a old macbook pro.