Recently I had a SharePoint installation that stopped writing log files without any clear reason. Restarting the timer service or the whole server did not solve the problem. The only thing I noticed was this entry in the event viewer:
Tracing Service failed to create the trace log file at location specified in SOFTWARE\Microsoft\Shared Tools\Web Server Extensions\15.0\WSS\LogDir. Error 0x0: The operation completed successfully. . Traces will be written to the following directory: C:\Users\SVCSPD~3\AppData\Local\Temp\.
Something seemed to be wrong with the log directory but the folder and its permissions looked totally normal. So I opened the Monitoring Settings (Central Admin -> Monitoring -> Configure diagnostic logging), change the path of the trace log to c:\temp and back to its normal location. As soon as I saved the second change, log files started appearing again.