Macbook "No entry" sign at startup (Grey screen)
Hi, when I try to start up my 2011 Macbook Pro I get a "No entry" sign that sometimes switches between the "apple" logo and then occasionally, but very rarely will I see a "folder with a ?". Is there anything I can do so I can get my computer working? I have OS X 10.9.1 and from what I remember a disc didn't come with my computer when I bought it new (so I can't insert a disc to install os x).
Side Note: I am posting from my computer that I have talked about above. This is a very good sign, however I know it'll get slow soon and then I'll have to reboot it only to get the grey screen again. (After turning it on and off 100 times I finally was able to get to use it this time).
MacBook Pro, OS X Mavericks (10.9.1)