Aero Peek not working or not available

To solve this issue , first try :
the Aero troubleshooter ( Control Panel-->Troubleshooting-->Appearance and Personalization--->tick the Display Aero desktop effects-->In the Troubleshooter dialog, click the Advanced link and place a check mark in the Apply Repairs Automatically option)

Or

Check the GP(Group Policy) settings, at CMD prompt type :
gpresult -v > c:\gpresult.txt