I have already tryed the .Tribler folder underC:\Users\X\AppData\Roaming.Tribler … nothing on it, so sorry.
The log should be in Roaming, next to .Tribler if it’s not there, you will have to wait for the next build with improved logging.
BTW, we just finished installing a windows 10 machine for testing and we have reproduced this issue, so we should have it fixed on the next RC.
The next RC may work on XP as a side effect for some other fixes in case you want to try it. 