Your pc must be hibernating or at standby for auto wake.
click Start -> All Programs -> Accessories -> System Tools -> Scheduled Tasks.
In the resulting Properties dialog box, click the Settings tab, check Wake the computer to run this task, and click OK.
click Start -> All Programs -> Accessories -> System Tools -> Scheduled Tasks.
Double-click the "Add Scheduled Task" icon to launch the Scheduled Task Wizard, and click Next. Select a program you'd like to run when your system wakes up (or u can simply select explorer.exe if u have no choice), and schedule the task. On the wizard's last page, check "Open advanced properties for this task when I click Finish" before clicking Finish.
In the resulting Properties dialog box, click the Settings tab, check Wake the computer to run this task, and click OK.