Hii dear
As I mentioned in the previous comment I had the same problem, I tried so much to fix my laptop, I checked it by some Anviruses which have their own startup with out the need of windows, I found some viruses by using them, I just knew that this problem had been caused by a virus, I do not know if the viruses I found and cleaned that way played a critical role or not, Any way after all I still had that black screen with the cursor, there was a change every time I powered on my laptop, for example some times it asked me to check the hard drive C, after checking there was some deleting and restoring process, then some thing happened, I just had a window in the black screen which was saying that the there is a problem with the log in page, there was nothing else, by pressing F10 when powering on the laptop I tried to restore my system to a restore point, I tried all the restore points but there was always a problem which make the system unable to restore itself, any way by telling all this thing I am gonna tell you I did my best just to bring back my system, I was unsuccessful.
At the end I used a "Windows live" cd, you can find it in any cd shops, I just copied my datas in an external hardware and I resored the system completely by pressing F10 and selecting restore C:
now every thing is good, as I have heard it is a kind of terrible virus which causes this disaster,