Hi Wilkoluke,
This appears to be an issue with the Air Temperature Sensor which is not there in Dell XPS 700. Dell Optiplex 745 system includes an air temperature sensor built into the control panel of the system. The sensor measures the temperature of the air pulled into the system and adjusts the system fans accordingly. You are not able to monitor the system temperature using this sensor; it is strictly a behind-the-scenes function.
You may notice an increase or decrease in noise levels from the system depending on the surrounding room air temperature. The temperature sensor is located near the front fan on each of the four chassis. The locations are as follows:
The image below shows the air temperature sensor on the SFF chassis. The two-wire cable runs across the bottom of the chassis and connects to the I/O panel.
If the cable from the control panel to the system board is disconnected, the system displays an error "Alert! Air temperature sensor not detected". This message indicates the system did not detect the sensor or the cable is disconnected. Reseat the cable and reboot to see if the message still appears.
If the temperature of the sensor rises above 42 degrees C (107.6 degrees F), the system logs an error (Air Temperature Out of Range) in the Event Log accessible through System Setup. The air entering the customer’s system has exceeded the 42 degrees C standard, and the system must now compensate with increased fan activity and noise.
Hope this helps. Please reply if you have any questions.