Well, yes your machine shouldn't have any problem with any game. Virus... maybe?
I installed a couple of cars, and after I installed this McLaren mod, the game will simply freeze after some point (and I assume it is the point when the game spanws an Infernus, which is the car replaced by McLaren). So yeah, some mods cause problems. But I haven't heard of this type of problem. Maybe it's a virus, or your Hard Drive is fragmented too much.
Try defragmenting your Hard Drive(s). It could take a while though.
Re-install, that's my suggestion for your last resort. Save all your mods neatly in folders. Uninstall the game, restart, refresh, and then install the game again. Don't worry your save game shouldn't get deleted with all the other files, but if you're not certain you can backup the save game at anytime.