Thank you for your replies.
I did verify the game files and that helped, instead of a black screen, I got the regular start-up screen.
- I have uninstalled the game, and deleted the C:/Program Files (x86)/Steam/steamapps/common/ cities II folder.
- Reinstalled the game.
- That worked partly as it took a while to load all the mods
Then I got this error message
[ERROR] Collection was modified; enumeration operation may not execute.
InvalidOperationException: Collection was modified; enumeration operation may not execute.
at System.Collections.Generic.HashSet`1+Enumerator[T].MoveNext () [0x00013] in <a314714511a14f84b853c03efd8682b8>:0
at Colossal.IO.AssetDatabase.AssetDatabase+<GetAssets>d__71`1[T].MoveNext () [0x00137] in <93949817766a42c1a3702853294a1fe1>:0
at Colossal.IO.AssetDatabase.AssetDatabase.<SaveSettings>b__76_0 () [0x000d9] in <93949817766a42c1a3702853294a1fe1>:0
at Colossal.IO.AssetDatabase.AssetDatabase.<SaveSettings>b__76_0 () [0x001a5] in <93949817766a42c1a3702853294a1fe1>:0
at Colossal.TaskManager+TaskQueue.RunNextTask (System.String name) [0x000b5] in <9b39602b6fff470f975256002258cf9c>:0
Colossal.Logging.CustomLogHandler:LogFormat(LogType, Object, String, Object[])
UnityEngine.Logger:LogFormat(LogType, String, Object[])
Colossal.Logging.UnityLogger:Log(Level, String, Exception)
Colossal.Logging.UnityLogger:Error(Exception)
Colossal.<RunNextTask>d__11:MoveNext()
System.Runtime.CompilerServices.MoveNextRunner:InvokeMoveNext(Object)
System.Threading.ExecutionContext:RunInternal(ExecutionContext, ContextCallback, Object, Boolean)
System.Threading.ExecutionContext:Run(ExecutionContext, ContextCallback, Object, Boolean)
System.Runtime.CompilerServices.MoveNextRunner:Run()
System.Threading.Tasks.AwaitTaskContinuation:InvokeAction(Object)
System.Threading.Tasks.AwaitTaskContinuation:RunCallback(ContextCallback, Object, Task&)
System.Threading.Tasks.SynchronizationContextAwaitTaskContinuation:Run(Task, Boolean)
System.Threading.Tasks.Task:FinishContinuations()
System.Threading.Tasks.Task:FinishStageThree()
System.Threading.Tasks.Task:FinishStageTwo()
System.Threading.Tasks.Task:Finish(Boolean)
System.Threading.Tasks.Task:TrySetException(Object)
System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1:SetException(Exception)
System.Runtime.CompilerServices.AsyncTaskMethodBuilder:SetException(Exception)
Colossal.IO.AssetDatabase.<<SaveSettings>b__76_0>d:MoveNext()
System.Runtime.CompilerServices.MoveNextRunner:InvokeMoveNext(Object)
System.Threading.ExecutionContext:RunInternal(ExecutionContext, ContextCallback, Object, Boolean)
System.Threading.ExecutionContext:Run(ExecutionContext, ContextCallback, Object, Boolean)
System.Runtime.CompilerServices.MoveNextRunner:Run()
System.Threading.Tasks.AwaitTaskContinuation:InvokeAction(Object)
System.Threading.Tasks.AwaitTaskContinuation:RunCallback(ContextCallback, Object, Task&)
System.Threading.Tasks.SynchronizationContextAwaitTaskContinuation:Run(Task, Boolean)
System.Threading.Tasks.Task:FinishContinuations()
System.Threading.Tasks.Task:FinishStageThree()
System.Threading.Tasks.Task`1:TrySetResult(VoidTaskResult)
System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1:SetResult(VoidTaskResult)
System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1:SetResult(Task`1)
System.Runtime.CompilerServices.AsyncTaskMethodBuilder:SetResult()
System.Runtime.CompilerServices.AsyncValueTaskMethodBuilder:SetResult()
Colossal.IO.AssetDatabase.Internal.<DisposeAsync>d__5:MoveNext()
System.Runtime.CompilerServices.MoveNextRunner:InvokeMoveNext(Object)
System.Threading.ExecutionContext:RunInternal(ExecutionContext, ContextCallback, Object, Boolean)
System.Threading.ExecutionContext:Run(ExecutionContext, ContextCallback, Object, Boolean)
System.Runtime.CompilerServices.MoveNextRunner:Run()
System.Threading.Tasks.<>c:<.cctor>b__7_0(Object)
UnityEngine.WorkRequest:Invoke()
UnityEngine.UnitySynchronizationContext:Exec()
UnityEngine.UnitySynchronizationContext:ExecuteTasks()
So, at least I get the game running again, but its not playable yet because I have tried clicked okay and continue but the game crashes quite fast after this error.