iMac not powering up

Check to make sure that the power cord is snuggly plugged into the back of the iMac.

For more things to try, see > If your Mac doesn't turn on - Apple Support

Carry den.thed's suggestion one step further and unplug the power cord from the back of the iMac, let sit for a minute or so, plug back in and try again. Unplugging and plugging back in to the outlet should do the same but it won't hurt to check.

Have you checked the power cord try verify it's OK?

Did the carpet installers use any power tools? Make sure the outlet has power.

And try try the iMac in another outlet. Try another device in the same outlet, etc.