If standby also fails, then the power management drivers could be corrupted.
Reinstall the power management drivers.
1. Click Start, select Control Panel, and then choose Performance and
Maintenance.
2. Click the System icon to open the System properties window.
3. Select the Hardware tab and click Device Manager.
4. Click the plus (+) sign next to System Devices.
5. Right-click the ACPI Fixed Features button and select Uninstall.
6. Restart the system.
This should work.
Regards
Selvaraj Shanmugam