Whats your system spec's, also how old is the PC as its a known fact that as PC's get old they start to fail more and more at the silliest of things even things it has done loads of times before with no probs.
But tbh it could be simple thing like overheating or corrupt game files.
There SEEM to be some issues with the servers. I have the same problem if i log in during times of high lag (wich seems to happen in the last days, but thats another thread). It freezes during map - loading?