Your problem description is pretty generic (my server is non responsive sometimes) and the Bad Me is tempted to reply, you probably have a performance problem to resolve 😛

Questions that come to mind include:

1. Is it a single database that is non-responsive or is SQL totally non-responsive?

2. What do the jobs do? Index maintenance, Backups, ETL, ...?

3. Are there Non-SQL (heaven forbid!) applications such as Exchange, IIS, File Shares, etc. on the server?

4. Have you reviewed the SQL Error log and Windows Event logs to see if any entries correspond to the event?

5. Is there an application that runs a big report each day?

6. Do you see any evidence of memory pressure?

7. Does disk activity increase significantly?

I am sure there are many more questions that others might suggest but at least answering a couple of these will get you on track to either eliminating or identifying a problem source.