Need some computer help!

[Italian Stalion]

I have with me a custom built computer, my problem is that It freezes frequently in some games, some more than other.
My specs are:
CPU: AM3 AMD 440 RANA 3ghz x3
GPU: Saphire hd 5670 1gb
RAM: 2x1 dual channel 1600mhz ddr3 Gskill (in bios made sure it was running at max speed)
PSU: coolermaster 460w
MOBO: asus m4a785td m evo (micro atx)
FANS: 1 80m intake 1 120m output

at first I had unlocked my cpu to 4 cores but i noticed the freezing issue worsened so i switched that back to normal.
I had my GPUs memory mhz overclocked a bit because it for some reason gave me a 10 fps boost in some games i noticed if i increased the core clock even a little bit (15mhz) games would fail to run or crash very quickly so i undid that very quickly. I set my gpu to default settings to see if that would help my issue but it did not.
I did do some overclocking attempts but my system was very unstable (basicly i messed with the voltages, I knew what i was doing of course but i hope this information helps anyway.)
I tried lowering my ram speeds and switching ram slots but that didnt do anything.

Basicly what happens is in the middle of a game the game will freeze then show a grey screen for like 5 seconds then go black again and then continue the game. Other times it will just straight up freeze, black screen and ill either crash to desktop or have to restart my computer. This happens very often in hl2 ep2 and ruse. when i play tf2 the problem usually shows up after 3 hours of play. Ive already made sure that my system isn't using to much energy for my psu to provide.

THANKS GUYS
PS. sorry about grammar wrote this in a hurry

 

[Skorpyo]

Put everything back to stock speed and tweak it up little by little.Otherwise you are just shooting in the dark. Also, your cooling system needs to be VASTLY improved.

Try another power supply while you are at it. Lots of strange, little things can happen when one goes, flaky.

 

[Eri]

Make sure you have almost no dust, and like ^he said, make sure everything is properly cooled.

 

[Italian Stalion]

I did put everything back at stock speed except for the ram but when i tried changing it, it didn't change anything (stock speed was 1333 changed to supported 1600 mhz) i dont believe its heating as when i play hl2 ep2 it freezes every 20 minutes whilst i can play tf2 for hours and be fine.

 

[TheComedown]

Put everything back to stock speed and tweak it up little by little.Otherwise you are just shooting in the dark. Also, your cooling system needs to be VASTLY improved.

Try another power supply while you are at it. Lots of strange, little things can happen when one goes, flaky.

This, set everything to default, overclocking with only stock cooling isn't that bright, also your PSU could be lacking a bit specially if your trying to overclock.

Again as someone said, check for dust and improve your cooling.