In cooperation with the U.S. Consumer Product Safety Commission , Lenovo is voluntarily recalling 160,000 ThinkCentre M70z and ThinkCentre M90z all-in-one (AIO) desktop PCs worldwide sold between May 2010 and January 2012. Lenovo has determined that due to a failure of the power supply in the affected All-In-One PCs, the system can overheat posing a fire hazard. Lenovo has received two customer reports worldwide of fire that resulted in damage to the PC.
Lenovo highly recommends you unplug that bad boy and quit using it NOW. Click on over to their site and provide your machine type and serial number to see if you need to get the power supply replaced.