Can someone please help me. Whenever I turn on my computer the screen is just blank. The keyboard is not functioning. What causes this problem?

Need more info. Is it a laptop or desktop? Getting information off the Internet is like taking a drink from a fire hydrant. ~Mitchell Kapor ~

Desktop!

What have you already done for troubleshooting? Computers in the future may have only 1,000 vacuum tubes and perhapsonly weigh 1 1/2 tons. ~ Popular Mechanics, 1949~

We need more information. When you turn it on, are there any LED's that light up for the keyboard, hard drive, etc? If not, then the first thing to look at would be the power supply. If Your getting LED's to light up, then let us know what is lighting up.

All of the LED's are not lighting up except for the power button.

Even if the power button is lit, it can still be the power supply. The 12 volt rail could be okay, but probably the 5 volt rail is gone. Find an old power supply that has the same number of pins on the main connector, either a 20 or 24 pin, and just plug them then in ( you don't have to pull the old one ). You might want to pull the side of the computer off, and turn the pc on, and see if any LED's light up on the mother board.