Restart SQL service (if downtime is permissible) and connect via DAC.
use select * from sys.dm_exec_requests to see what requests that is executed against the databases. You will see wait types, wait resources, etc. It will give you more info then sp_who2. High CPU usage can be caused by a lot of reasons like:
Bad execution plans caused by bad statistics
Locks and blocks
DBCC CHECKDB
Index rebuild
etc
The below link provides more details on scripts for troubleshooting: