Without actually knowing what's happening, it's hard for anyone to help you. What happens when you try to connect? How far into the start-game process are you when you hit problems?

First basic things to try:

Remove the mods you have running. See how vanilla runs. That's always first port of call.

Verify the your game files as this can help clear bottle-necks.

Check with your host that things are working correctly as they might need to refresh something.

Something as simple as restarting your router may fix this.

Flush the IP.

Start Valheim as Administrator.

If you're able to connect at all but hit problems loading the seed, you might need to start a new one as your current may be corrupted.