DIAGNOSIS First, rule out the obvious: it's either the outlet, the power cord, or an internal fuse/safety switch has tripped due to a previous overcurrent (like a power surge).
FIX Check a different appliance in the same outlet to confirm it has power. If the outlet is good, trace the power cord for any cuts or damage. The most common fix is to unplug the unit from the wall for a full 5 minutes. This allows the internal control board to completely reset. After 5 minutes, plug it directly into the wall (not a power strip) and try the power button again.
IF THAT DIDN'T WORK There's a float switch inside that shuts the unit off if the internal drain pan overflows to prevent water damage. Tilt the unit back slightly (so the back is lower than the front) and try turning it on. If it starts, you had a drainage issue.
HEADS UP If the 5-minute reset and tilt trick do nothing, the control board or main wiring is likely faulty. This requires professional repair. Don't open the casing yourself unless you're qualified—there are high-voltage capacitors inside that can hold a dangerous charge.