SharePoint stopped working

I am getting critical alerts on the SBS 2011 console. The following errors are coming up: -

1. SharePoint 2010 VSS Writer service has been stopped.

2. SharePoint 2010 Timer service has been stopped.

3. SharePoint 2010 Foundation Search V4 has been stopped.

This is causing the Task system and everything else related to SharePoint to stop working. What is the cause and how do I fix it, thanks. Allawi