Lets try and see if any hardware is causing it wake up.
1. Click Start, and then type cmd in the Start Search box.
2. In the search results list, right-click Command Prompt, and then click Run as Administrator.
3. When you are prompted by User Account Control, click Continue.
4. At the command prompt, type powercfg /-lastwake, and then press ENTER.
you should see something like...
Wake History Count - 1
Wake History 
Wake Source Count - 1
Wake Source 
Under Device it should show you what is waking the PC up.
Let us know how you get on,