Diagnosis
The water supply is either off, the inlet valve is clogged, or the steam generator/heater is faulty. Check the simplest things first.
How to Fix It
Verify the hot water valve behind the dryer is fully open. Disconnect the water supply hose from the dryer inlet and check for flow into a bucket. If flow is good, the internal water inlet valve (part #5304520501) is likely clogged with sediment and needs replacement or cleaning.
If That Didn't Work
The steam generator (a small tank with a heating element) may have failed. It's located inside the dryer behind the front or rear panel. Testing requires a multimeter to check for continuity on the heater element.
Heads Up
Only use a standard washer hose, not a braided stainless steel hose, for the dryer's water supply. The braided hoses have a flow restrictor that can block the low water volume needed for steam.