<Shrug!> Could be anything.
From what you say it's probably a software bug rather than hardware falling apart, but whether it's in the operating system, the game, some driver, the firewall ... is anybody's guess.
Well, OK, there are some things you can do, such as
(1) install the debug symbols for the operating system
(2) run it up under a debugger
(3) when it crashes get a stack backtrace
which might, or might not, help you identify which components are involved in the problem, but this sort of stuff is typically beyond yer average punter (I can do it for you of course, at £xx/hour, no results guaranteed at all, but most people don't take me up on such offers).
Or just switch off and/or install unnecessary crap and see if it works on a more basic machine, but you're poking around in the dark here. One might try some of the following, pulling your network cable if you're really relying on stuff on the local host to protect you from malware:
(a) disabling antivirus, personal firewalls, suchlike (zonealarm is a horrendous nasty, but there are plenty of others you could have)
(b) uninstalling the above
(c) junking your screen driver and going back to whatever basic one the operating system provides (you don't say which operating system you're running, which might, or might not, have helped)
(d) switching off or uninstalling any services you don't recognise that aren't contributing to FS2004.