Virus blocked internet how can I scan my computer

If malware gets past your AV with it’s current signatures (be it Webroot or any body else’s), you’re stuck.
No way to update the database, should new virus definitions include protection for the new threat.
I would DL (on another machine) one or more of the numerous cleanup tools, and hopefully be able to run them on the infected box.

Its just strange that they dont have a way to scan if offline. Most programs...I use avast on my home machine can scan even if infected or even offline or by using a boot time scan if needed.

I understand your concern. But as stated, if malware somehow gets past Avast, and subsequently disables internet connectivity, you cannot DL latest definitions that may address the new threat.
I, too, was apprehensive about the lack of local database, but virtually all the threats today are web related; DLs from web sites, drive-bys, opening infected email attachments, etc. all of which require internet connection.
No internet - no protection, but no infection either.
Possible reasons for concern: Infection via removable media when not internet connected. Unzip / execution of an email attachment after disconnect from internet.

Here's how Webroot functions while offline - any new process it sees gets automatically monitored for bad behavior, and all changes it makes are journaled in case it need to roll back those changes after Webroot gets back online to talk to the database.  Also if it detects any really bad behavior like the process trying to replicate or muck around in the registry or system files, then it will prevent those actions from happening.

Which is why some prefer to have also installed (as on demand only) MBAM or similar.

Thank you, nic, for the succinct explanation.

In the end, it makes sense. I guess at first impression its just a little difficult to understand. Thanks

Sure thing, glad to help.
 
Yeah the way Webroot functions is quite different, which can take a while for people to grok.  A lot of the AV testing companies have trouble evaluating our software with the tests geared towards traditional signature based detection.  We try to work with them to come up with methodologies that work better with our software.  

You might try SafeMode with networking!?