I generally close as many apps as I can when installing an anti-virus which helps to ensure the installation goes smoothly. Some programs and security tools monitor installation activity and can cause problems. You need to reboot after installing avast and the programs you temporarily close will startup normally afterwards.
BTW, SpywareBlaster does not
run in the background. Instead it only requires installation and then enabling of all protection. After that you only have to check periodically for database updates using the built-in "Check for Updates" feature and then enable all protection again. SpywareBlaster blocks spyware tracking cookies, restricts the actions of potentially dangerous sites by adding a list of sites and domains associated with known spyware, advertisers and marketers to the browser's "Restricted Sites Zone" and prevents the installation of ActiveX
-based malware, browser hijackers, dialers, and other potentially unwanted software.
If you are not sure how to use SpywareBlaster, please refer to the How to use SpywareBlaster to protect your computer