BLAK SCREEN AND READ NO O/S

Do you mean when you power on now, you get a black screen that reads "No Operating System" ?

If you got a Blue Screen of Death, what was the error?
What had you just been doing when it happened?

What is the make and model and age of your computer?

As the old saying goes - '[i]It's all in the detail![/i]'. ;)

1. you have no OS installed

2. you have a HDD password, and you typed it in wrong too many times...