After login

Hello,
My computer a Dell inspiron 530 with windows Vista 2008 will get to the log in screen and let me log in but after i do the screen goes black and i can only see my mouse, i had found a way to get past it by Ctrl, Alt, Delete the going to file and typing in "explorer" and it fixs its self. But im now having to do this every time, any ideas on how i can fix this permenently?