I started BigQuery trial account just before and created sample table using a source with Drive URI & CSV.
When I clicked my uploaded table, it shows table information like schema and details.
I remember that there was a preview menu but I can't find it now. 
Is there anyway to activate table preview menu?
When your table is created from a file from Google Drive, by default "Preview" tab is not available since it is considered as an external table. I tested it to verify the behavior.
Created table sourcing from Google Drive:
What I could suggest is to load your data from Google Drive to BigQuery, so the "Preview" tab will be available. Also if you load your data in BigQuery, running queries will be faster compared from querying the table externally.
