You're going to have to run a DBR now regardless of doing anything. Once you've stopped the process of loading, even with a white screen, it means that you've corrupted something. A white screen means the program is not responding to user input, but is busy in the background. The first load after an update is the longest. The content is being cached and scripts are being compiled. Depending upon how much content you have, including DLC, the process can take sometime. Once cached, the process becomes quicker afterwards. The problem now is after running a DBR, you'll have to go through this process all over again.
After running the DBR.
Open Content Manager.
Check for faulty assets. View errors and warnings. Faulty assets should disappear. You may have to exit to installed and come back to refresh. If there's anything faulty left, it needs to be investigated further.
Check for updated DLC. This may remove many outdated assets and also solve many, many missing dependencies as well if there are any.
Check for open for edit assets, revert those to original if there are any.
Check for updates, install those and remove obsolete assets, for those assets not part of the DLC or built-in.
Defragment your hard drive, highly recommended, before loading up Trainz again.
This is the process I used when I updated and I have no issues like that at all.
