Crash on startup, new install
Are you shutting down all non-essential programs (especially anti-virus) before starting the game? Firewalls can cause conflicts (generally on startup or loading screens) and overlays from graphics tweaking/monitoring programs or chat programs can also cause issues.
In the launcher settings, try switching to DirectX 11, rather than Vulkan, and see if that gets the game to start.
Try exiting out of the Steam client, if applicable, and starting the game 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.
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.
Try right clicking and holding on the bg3_dx11.exe / bg3.exe executable, then hold Shift down, release the right mouse button and select Run as administrator, continuing to hold Shift until the splash screen comes up. Holding Shift prevents the game from taking focus when loading, and can avoid certain resolution or DirectX/Vulkan issues. Holding Shift when starting the game from the launcher may do the same thing.
If you are using a program such as Process Lasso to adjust the core affinity for games (for example to have games and system processes run on different cores), try disabling it to restore the default (all cores).
One person reported a conflict with Process Lasso's 'core engine' being on, even with the settings for the game restored to default.
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.
With the GOG version, in the (optional) Galaxy client, select the game, then the settings icon at the top right (beside the Play button) and under Manage Installation select 'Verify / Repair'.
Especially if you have a relatively high desktop resolution, you can try temporarily lowering it, to limit what the game will auto-detect. If that allows the game to start, you can then exit and restore your desktop resolution.
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')
- check the information under the 'General' tab below the list of events, starting with "Faulting application name..."
Check for updated graphics drivers, and Windows updates in general.
If the game gives a VC related dll error when starting from the executable, try installing the 2019 Visual C++ redistributable (64bit). In the Control Panel, Programs and Features, try right clicking the MS VC++ 2015-2019 redistributable entries (32 bit and 64) and select Uninstall and then Repair. If that does not help, repeat the process but continue with the uninstall, reboot and then try installing from the redistributable installer.
C:\Program Files (x86)\Steam\SteamApps\common\Steamworks Shared\_CommonRedist\
C:\Program Files (x86)\GalaxyClient\Dependencies\__redist
Try browsing to the 'C:\Users\<UserName>\AppData\Local\Larian Studios' folder and rename the 'Baldur's Gate 3' subfolder. The easiest way to get there would be to copy the line below into the location bar in Explorer and hit Enter.
This folder contains the saved games, configuration files and a level cache folder. Normally it would be best to rename the the folder for troubleshooting purposes, but if you don't have any saved games that isn't an issue.
Next, extract the replacement folder from this download into your '..\Local\Larian Studios' folder, to see if that will let you start the game.
The graphicSettings.lsx file is set to 1280x720 Windowed mode and Very Low quality preset, which you can change in the options (manually, or hit autodetect) if this gets the game working (as well as optionally create a new profile).
If the game still crashes, you can delete the replacement BG3 folder.
NOTE: prior to Patch 7, the configuration files, profiles and saves were stored in the Documents folder for the current user account. In that case, you can follow the same procedure, but extract the replacement folder from this download into your '..\Documents\Larian Studios' folder.
Try doing a clean boot and then test the game. Click Start, or hit WinKey-R, type in msconfig and hit enter; in the General tab, click Selective Startup, uncheck Load startup items (if required) and leave Load system services and Use original boot configuration options checked. Next, click on the Services tab, check the box to Hide all Microsoft services, then click the Disable All button (maybe make a note of which are currently enabled/disabled), then click OK and reboot the computer.
Run msconfig again to switch back to the normal boot configuration.
If that doesn't help, please contact support with a dxdiag report (WinKey-R, type in dxdiag and hit enter, then when it finishes loading click on the 'Save All Information...' button and save the report somewhere handy). Also check the '..\Baldurs Gate 3\bin' folder (and '...\bin\db\attachments' or “...bin\db\reports”), and if there are any CrashDump files being created, zip a few together to include.