Does the HOME button work (that's the round one on the face of the phone). If it doesn't there's nothing you can do. The SLEEP button is on the top edge of the phone. Does that work?
Do the following, EXACTLY:
- Reboot your computer
- Disable your antivirus and firewall
- Launch iTunes and make sure it is version 11
- Connect one end of the iPhone cable to a USB port directly on your computer, NOT to a hub. DO NOT connect the other end yet.
- Disconnect all other USB devices except mouse and keyboard.
- On the phone hold BOTH buttons for EXACTLY 10 seconds, until the screen turns black. If an Apple logo appears, you held too long; do it again so you have a black screen, then release ONLY the top button (SLEEP) and keep holding the round button.
- While holding the round button connect the cable to the phone AND KEEP ON HOLDING THE ROUND BUTTON.
- Watch iTunes. It should display a message saying that a phone in Recovery mode has been detected. You may have to hold for a minute or two until this message appears.
- Once the message appears release the round button and the phone should restore.
On step 8 if the message hasn't appeared after 2 minutes there's a problem with your computer that you will have to resolve first. See: http://support.apple.com/kb/TS1538
If anything doesn't work as I described tell me which step and what the outcome was.