The Larian Launcher is crashing
Are you shutting down all non-essential programs before launching the game? Things like anti-virus, firewalls, overlays from graphics tweaking or monitoring programs, as well as chat programs, have all been known to cause issues.
Try verifying local files: in the Steam library, right click on the game and select Properties, switch to the Local Files tab and then click on the 'Verify Integrity of Game Files...' button. If you are using the GOG version, in the Galaxy client, select the game, then the settings icon at the top right, beside the Play button and under Manage Installation, select 'Verify / Repair'.
Try starting the launcher directly from the '..\SteamApps\common\Baldurs Gate 3\Launcher\LariLauncher.exe' executable. For the game, try optionally exiting out of the Steam client and starting it directly from the '..\SteamApps\common\Baldurs Gate 3\bin' folder, by right clicking the executable (bg3.exe for Vulkan, or bg3_dx11.exe) and running as administrator.
For the game, try right clicking the executable, select Properties, switch to the Compatibility tab and check off the 'Override high DPI scaling behavior' option (set it to Application), run as administrator and disable fullscreen optimization, and maybe set a Win 7 or 8 compatibility mode. In Windows 7, check off the option to 'Disable display scaling on high DPI settings', disable desktop composition and run as administrator.
If you get a .Net error message trying to start the launcher from the executable, in Windows Control Panel, Programs and Features, try right clicking the Microsoft Windows Desktop Runtime entry (6.0.x), select Uninstall and then Repair. If that does not help, repeat the process but continue with the uninstall, reboot and then try installing the .Net Core redistributable from below. The minimum required version is 6.0.11, which can be found in the Steam install folder:..\SteamApps\common\Baldurs Gate 3\DotNetCore The most recent version can be found here.
If the launcher worked previously, try copying and pasting %LocalAppData%\Larian Studios into the location bar in Windows Explorer, hit Enter, and then in that folder delete the 'Launcher' folder and try starting the launcher again. If that helps, the first time the launcher starts it may take a little longer, as the cache is rebuilt. This is less likely to help with a new install.
If you are still having issues, you can always run a crash analysis. If you check the Event Viewer, does that give an error code or 'Faulting Module' file name that might help identify the cause of the crash?
Click Start (or WinKey-R), then type ""event viewer"" into the search box. In Windows 10, 'event' should bring up 'View event logs'. After starting the Event Viewer, expand 'Windows Logs' in the left column and select 'Application'. In the center column, look for a recent error for the game (maybe sort by Date and Time, or search for 'bg3') Lastly, check the information under the 'General' tab below the list of events, starting with ""Faulting application name...""
Hopefully by this point the issue has been solved but if you are still experiencing trouble, there are a few files that you can send us and we'd be more than happy to take a deeper look.
We would need a dxdiag report and a run log. To obtain the dxdiag, use the WinKey-R, and type in dxdiag and hit enter. Then when it finishes loading click on the 'Save All Information...' button and save the report somewhere handy. For the run log, copy and paste %LocalAppData%\Larian Studios\Launcher\Logs into the location bar in Windows Explorer, hit Enter, and locate the runlog.txt file, contact Support and include the file in your report.