Desktop goes on, but the screen reamins blank

Hello, everyone.

Let me start how did the problem came up to me and said hi.
I usually leave the computer running overnight and set it to turn off after 2-3 hours. I use program called "CWK" and it makes the computer stand by after 3-4 hours. I leave a game on but the computer works like usually.
Few nights ago I left it like I do everyday. I woke up and I turn the computer on, the fans go on everything works, but there is nothing on screen.

The computer starts up and is at 100% meaning, if you had 100000x programs open and the CPU was busy the whole time with the processes. As I turn it on, the monitor doesn't react, like nothing ever happened, the computer reamins at 100% until I turn it off. I disconnected the computer, looked inside, unplugged and plugged in cables again and nothing happens. The monitor is 6 months old so there is no way it is broken, any ideas?

It happened to me before but my brother fixed it, I don't remember how, he did something inside the computer.

Maybe I should connect HD to SATA1 instead of 0?

My computer is:
Gateway 770gr (i think)
p4 3.4ghz
1gb ram
geforce 8800gt

OH, the mouse and the keyboard doesn't work either I don't think any of the USB's work.

Thank you for every response.
Help greatly appreciated.