prohibitory symbol

I was finishing an edit and while it was rendering the screen went black. After a full blown panic attack, I tried to turn it off and turn it back on and nothing happened. After I went away for about 30 minutes or an hour, the prohibitory symbol came up. It flashes about every 60 seconds. If I turn it off and try to turn it on again nothing and then after about 30 minutes or an hour(or longer, I'm not sure), the symbol comes back on and flashes every 60 seconds. Can anyone help? I have about 3 months worth of editing that is on this computer. I do have file back ups but I made about 100 changes on that last day of editing and did not back that up. I really don't want to start all over. Thanks