The "link" is often a network link. If your ISP routes your traffic through a congested node, or if your router struggles with IPv6, the game client will time out trying to fetch the us.actual.battle.net or eu.actual.battle.net manifests.
If the game lacks the permissions to write new data to your drive, it will hang indefinitely. Preparing game data - Technical Support - SC2 Forums starcraft 2 preparing game data link