Before doing anything:
+ Make Vsynch ON (recommended 60hz).

Fixes:

+ windows button + R to open "RUN" type - %appdata% then go to these folder Roaming > WB Games > LEGO® Harry Potter™ > open pcconfig.txt and change this DesiredDynamicLightQuality 2 to DesiredDynamicLightQuality 0. (this should fix dark tower level crash.)
+ There is another chance you can fix this level by playing 2 player Co-op with splitscreen, you need to split up and there is low chance that this won't trigger a crash.


+ Click on the speaker and find the speaker properties and choose the advance tab and then change your device to 16 bit or 24 bit 44100Hz and 48000Hz.


@Pod mentions - in compatibility tab on games properties, change compatibility to Windows XP Service Pack 3 or other one + run as a administrator.

Resolution can impact crashing so try lowering resolution in general.


+ THIS IS FINAL SOLUTION BUT BE WARNED!:
In steam - open game settings
Game Menu > Properties > Set Launch Options
Type in:
- dxlevel 90
This makes DirectX 9 version of the game, BUT IT COULD CORRUPT YOUR SAVE FILE SO ONLY DO THIS IF YOU'RE STARTING NEW GAME.