Android/Samsung Galaxy Duos lockout problem

Hello people! I just got about 2 weeks ago a Samsung Galaxy Duos phone with Android 2.3.6. After I discovered the world of applications, I installed like 40 apps in a day and the trouble begined: at regular intervals screen is going blank, the phone vibrates once and then it seems like it does some sort of "cold reboot", the GSM signal re-appears as if it was booting but without the samsung logo. It stays off for 10 seconds and the "rebooting" takes like 20 seconds.
I had uninstalled apps like hell and after restarting still does this. But After I take out the battery, it operates normally. Next day I installed 20 apps, same problem, same solution only this time I needed to also use included task manager to turn off tasks like Yahoo messenger and likes.
I tried to use advanced task killer, I tried Watchdog to catch an app that is "rogue" and eats processor (only showed 30% usage by Android system), I even put the phone in the fridge to cheel out the processor, no effect. Now, I installed 10 games, the problem re-emerged and this time it was much harder to get rid of it. Finally I used Airpush detector and removed a game, and also removed all the casino games. Finally it works, no lockouts!
Pls advice what could be the problem, what should I do if it re-appears and how to avoid it in the future. I learned to be very carefull when installing an app and also installed Lookout Security who scanned 250 apps and found nothing. I am interested how can I control which apps and services start with the boot (no need for Skype/Yahoo, pedometer etc., and in the apps settings the boot options are grayed out). I mention the phone is not locked to my carrier. I am not sure about "rooted". I guess not. I tried with superoneclick and cannot find driver, guess the phone is not supported.
Thanks in advance to anyone who can provide help!