4. no but i have this old install that always worked no problem and never had any freezes. Now it's freezing, so it's something else for sure.
Software works pretty much like hardware. Yesterday it worked fine, today it doesn't.
Which means, if you think further, if your OS or browser can be affected and "altered" by some other software, so does a game (specially UT since it has all the files spreaded around, instead of some games which have either all integrated into a single app or a very low amount of packaged files).
It happens that UT is really a vulnerable game which can be damaged: by a server, by a mod, by some external software, etc.
So since it only happens with UT, I would say that it's most likelly UT itself (it can be now corrupted).
So you can have an idea on how vulnerable this game is to servers and mods, I have 4 UT installs in my system: a "virgin" one (no mods or anything), the main one (where I develop and test my mods, and play on servers), the ONP one (just to play ONP lol), and a heavilly screwed one which I just didn't delete yet due to the amount of resources and mods there (which was in times healthy as yours, but it got screwed by mods, and perhaps by a few servers as well, but no by me for sure since I didn't even coded at the time rofl).
So:
Yes, in case of a "corrupted" file from the engine itself (core or others), that should solve the issue (as repatching replaces the old main critical files by the updated ones, so if there's anything corrupted, it gets replaced and therefore fixed, pretty much like if you were "repairing Windows").
However, if that doesn't work, install the game elsewhere (in another directory, partition, whatever place), just to test if the CPU goes to 100% and keeps freezing as well (since it can also not be related to a "main" file of the game).
It would be only an "external cause for sure", if that issue also happenned with other games or applications in your PC.