Diagnosis
This is an overheating shutdown. The projector's thermal sensor triggers a protective power-off. Primary cause is a clogged air filter or internal dust. Secondary cause is a failing temperature sensor or fan.
How to Fix It
Check and clean the air filter immediately (see fan noise fix for procedure). Ensure the projector has at least 6 inches of clearance on all sides, especially the exhaust vent on the front. Operate in 'Eco' lamp mode to reduce heat output. Monitor the internal temperature: in the menu, go to Settings > System Setup > Information > Lamp Temp.
If That Didn't Work
The thermal paste between the DMD chip and its heatsink may have degraded. This requires disassembly to re-paste. A faulty fan will show reduced RPM in the service menu. Enter the service menu (Exit button for 5 seconds) and check the 'Fan Speed' reading. It should be above 2500 RPM under normal load.
Heads Up
Do not place the projector in an enclosed shelf or near a heat source. The exhaust air temperature is very high. The shutdown cycle is protective—continuous overheating will permanently damage the DMD chip, evidenced by a permanent yellow or pink tint to the image.