No, if you back up the steamapps folder first. Move it out of the Steam directory, reinstall Steam, then move it back in. Your game files will remain and Steam will detect them automatically.
This could be due to corrupted local configuration files. Try deleting the "config" folder in your Steam directory (make a backup first). Also try clearing your browser cache in Steam: Steam → Settings → Web Browser → Delete Web Browser Data.
Steam requires an internet connection to initially launch and verify your account. However, once logged in, you can go offline: Steam → Go Offline. Your installed games will still work without internet.
This is often caused by corrupted graphics drivers or incompatible overlay software (like MSI Afterburner, Discord overlay, or RGB software). Try disabling these or updating your GPU drivers.
Default locations: Windows: C:\Program Files (x86)\Steam or C:\Program Files\Steam. Mac: ~/Library/Application Support/Steam. Linux: ~/.local/share/Steam or ~/.steam/steam.