Most probably you’re clean.
The first message refers to that infection, once cleaned, you’re clean. Avast send the file to Chest and nothing wrong with that.
You can schedule a boot time scanning or run a throughout scanning (including archives).
You can scan your system on-line for sure (see http://www.security-ops.tk/)

Definetivelly not…
Are you refering to Screen saver module of scanning or a common scanning by avast?