Open the registry & navigate to one of the following keys:
If you use the XP-style Start Menu:
"HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\MenuOrder\Start Menu2\Programs"
If you use the Classic Start Menu:
"HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\MenuOrder\Start Menu\Programs"
If there is a value named 'order' in the right pane, delete it.
Right-click the folder icon for the above-mentioned key and select 'Permissions....' In the
Permissions dialog, click 'Advanced.' In the Advanced Security dialog,
click the 'Add' button and the type your username when asked to select user or group. In the
'Permission Entry' dialog, deny 'Set Value' permission & OK your way out. This will prevent the
'order' value from being recreated when new programs are installed and explorer will default to
alpha-sort.