Did you find and delete the reboot.txt file Tech mentioned ?
If you didn't find it or it didn't resolve it.
You can also check this registry entry (right after computer restart):
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Session Manager, if it contains "PendingFileRenameOpertaions".
Check its contents and if there's only "reboot.txt" from avast4\setup folder, delete PendingFileRenameOperations, don't delete any other key.
Back-up (export) the registry key before you edit/delete, just in case.