You don't have to purchase, it is an offer that is all. You just need to re-register the free version for another year.
You are using an old version of avast7, last version of avast 7 was 7.0.1474 so you haven't been keeping it up to date.
Avast 8 has been released and I suggest that you do a clean install of avast 8.
- Download the latest version of avast, 8.0.1482
http://files.avast.com/iavs5x/avast_free_antivirus_setup.exe and save it to your HDD, somewhere you can find it again (if you didn't save your last download). Use that when you reinstall.
- Download the avast! Uninstall Utility, aswClear.exe
find it here and save it to your HDD (it has uninstall tools for 6.0.x and 7.0.x).
- 1. Now uninstall avast! (using add remove programs, if you can't do that start from the next step), reboot.
- 2. run the avast! Uninstall Utility from safe mode, first for 6.x if previously installed and then for 7.0, once complete reboot into normal mode.
- 3. install the latest version, reboot.
I would suggest that you save/backup your avast settings and restore them when avast 8 is installed. From the avastUI, Settings, Maintenance, Settings Backup.
See
http://forum.avast.com/index.php?topic=116245.0 for a little more on the new avast 8.