Unmountable Boot Volume

Hello, My desktop came unplugged and when I plugged it in a blue screen came up with unmountable boot volume on it.I tried restarting computer and pressing F8 but that didnt help. I even tried goin to safe mode but it wouldnt leave blue screen except when I went to safe mode it did go to black screen tried booting up but went back to blue screen it wont let me type anything in either. Thank you for any and all help...Beverly