How much disinformation here... Such game running problems have been already discussed many times in the forum, the info are already available.
About your case, you play the game with the software rendering graphic. Play the game and add-ons it's not recommended with that setting because can be problematic. As previously told you, update the graphic card, or change PC... The "Heap Overrun" and similar error messages are especially got when having too much add-ons in the game folder, but the quality that you've described isn't exaggerated.
The mm2.lock file gets automatically created everytime that you run the game, and when quitting from the game, it removes it. When the game gets a crash and shuts down, that file remains, obviously; it's made to advice, when the user do the next game launching, that previously happened a problem with the game working (it lets open the YIKES.RTF file, with some tips written). Run the game and manage the adjunctive .ar files though MM2 Game Loader program to let ignore all this thing.
And if you're running MM2 on software rendering mode, then any vehicle that has .tga format textures will crash the game giving a fatal error. (That's what my experience tells).
If it's so, it's a weird experience, because in the few occasions when I've played the game in software rendering using add-on cars that uses textures in TGA format I haven't got game crashes. Then, the game itself already uses the TGA format for some of its textures.