HomePod won't connect to anything

It’s not clear if you just tried restarting it or the hard reset Or which model of Homewood. The Gen 1 or 2 or a mini?

In any case if you’ve done the hard reset to no avail, try it again by leaving it unplugged for over a day to start

• You should ungroup any stereo paired HomePods first.
• Unplug HomePod for over 24 hrs
• Plug back in - wait 10 seconds

1. Unplug HomePod or unplug the power adapter for HomePod mini, wait 10 seconds, then plug HomePod back in.
2. Wait 10 seconds, then touch and hold your finger to the top of HomePod.
3. The white spinning light will turn red. Keep your finger down. 
4. Siri will say that your HomePod is about to reset. When you hear three beeps, you can lift your finger.

• After you reset HomePod, you can set up HomePod again.

Reset HomePod or HomePod mini - Apple Support

if it’s a case of it won’t set up again, first try restarting the iOS device you’re using to set it up.

Or it may still be connected to your iCloud account- on your iPhone in Settings - Your name- scroll down to see if it’s still listed and remove it, then try the set up again.

Set up HomePod - Apple Support