Hi Millie,
If you ever find a virus, then you should always perform a second antivirus scan with System Restore disabled.
Windows does not let you quarantine or delete virii that are in System Restore, so by disabling it will destroy the contents. By doing a second scan is just a precaution to take. Normally, by disabling System Restore and then rebooting followed by enabling will destroy the virii data.
But if you had done a System Restore before disabling it, then you would have got the virus back.
In your case you have done the correct thing by disabling System Restore, after finding a virus - I hope you have remembered to enable System Restore now...
By default Windows protects System Restore, this is why you cannot edit the System Volume Information directly.