GTA IV Alt-Tabs itself?

[Krieg]

Recently I learned how to mod GTA IV, mostly for vehicles, and weapons. It didn't change the stats, just the skin/model of it. And recently the game have been alt tabbing itself, so I uninstalled all the mods, it still does it. The weird thing is, it does it by itself, I'm not doing it, so I click on the IV icon (which indicates the game) and THEN it crashes. Why? I don't know. If anyone has encountered this...... problem, please let me know, or if you have fixed it, please let me know too. Thanks.
I haven't seen anything else pop-up whilst playing. I might have Firefox on sometimes to listen to some music, or to just have Background noise. I forgot to mention this as well, it only happens in specific spots, it's not random, I'll drive towards Bohan, and then it alt-tabs.

 

[Semtex]

I haven't had it do that. However, if this is the only game you've been playing then there's the question of: Is GTAIV effectively alt-tabbing itself, or is another program switching itself to the front? That would have the same effect because GTAIV or any other fullscreen program would get minimised to allow the other program to come to the front.