Some servers (such as the Dell PowerEdge T410) use IPMI (Intelligent Platform Management Interface) for management and monitoring. The lm-sensors package will not give you much useful information on these systems. Fortunately there is an IPMI package that can be used.
sudo aptitude install ipmitool sudo modprobe ipmi_si sudo modprobe ipmi_devintf
sudo ipmitool sdr # or sudo ipmitool sensors