The latest VPS update is checking for old program versions and if out of date will update the program as will, this would require a reboot.
I don't know if this was one of the things you read or tried. If you are continually asked to reboot, try this.
Operating system restart needed by avast message - First check the contents of the C:\Program Files\Alwil Software\Avast4\Setup\setup.log file, which should show you why it thinks the reboot is needed.
This could be solved, in some systems, by deleting the file C:\Program Files\Alwil Software\Avast4\Setup\reboot.txt
If that doesn't resolve it check this (running the uninstall utility as you did would probably have cleared this):
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.