Be sure to call it "MalwareBytes"!
MalwareBytes may detect some parts of the viruses that are no longer active on your computer (like registry entries). In order for a virus to be active on your system, it must have a set of instructions to follow. Generally these instructions are in files on your Hard Drive. Even if there are left over parts, as long as the main instructions are gone, the virus can not harm your computer.
If your sound is missing, you probably just need to reinstall your sound drivers. You can probably find these at your computer manufacturer's support web site.
If you decide to use System Restore to a point before the virus, you should be fine. However, this is assuming you really are restoring to a point before the virus was active. it's a good safety precaution to still double check your system using an up-to-date AV and AntiSpyware application.