Laptop screen goes black after inputting password

Morning, i have a Dell inspiron 17 with windows 8.1 installed its just over a year old and last week after a restart it loads windows fine until it asks for the final log-in password to take you to the desktop i enter the password then it goes black and all you see is a the mouse cursor which you can move about weirdly enough! system restore doesn't work but i can get in on safe mode if i do the power button reset 3 times. have tried a few solutions found online but nothing seems to work. please help!!