Any game i play, it either crushes or the entire computer freezes and makes a loud buzzing noise. I know that the 560ti come overclocked to 1000mhz. I have used MSI Afterburner to underclock them and still crushes(have tried all possibilities and combos and nothing works). So i decided to try my older GTX295 card and the same problem occurs. Can someone help me with this issue because its been driving me crazy for the last 3 months.
Based on your components, I would suspect the power supply first, and the motherboard second. Thermaltake makes excellent cases but not excellent power supplies. 800 watts is more than enough for that system, but not if it is poor quality 800w. I would get it checked out, or if you have another power supply to swap in, that would be the easiest way.
The second thing with the motherboard is that MSI is not the greatest quality either. It could be some capacitor or voltage regulator is failing.
A third suspect would be the video card. Gigabyte makes excellent motherboards, but their video cards are just so so.
It could still be the PSU. Even though it says 800 watts, it may not be supplying that, maybe never did. As they age, things go down hill. Of course a component in the PSU may have failed or is failing as well.
The other issue with low quality power supplies is that they can often supply "dirty" power. This also gets worse with age.
Once again, I would get the PSU tested if you have something like a Best Buy Geek Squad nearby or some other computer shop.
Think of the power supply as the mother of a computer. In Texas, we have an old saying. If mama ain't happy, ain't nobody happy.