What avast! version and VPS file (virus database) number, e.g. 4.7.1074 and 071202-0 (see about avast!) ?

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 may be solved, in some systems, by deleting the file C:\Program Files\Alwil Software\Avast4\Setup\reboot.txt