Try the below steps to check which program is causing this problem.
1. Click Start.
2. Click Control Panel.
3. Click Performance, Information and Tools.
4. On the left pane click Advanced Tools.
On the upper part of the window, just before “View advanced information about your computer’s performance” there is a small section which, in case something is wrong with windows 7, should report the following message: “Programs are causing Windows to shut down slowly”
5. Click on it and find out which program is slowing down your PC.