Instability of my 820D @ 4.2ghz

[Guga]

I'm running my system at 4.2 ghz for last month, and latelly it start rebooting random.

But its not allways the same way.

I can play Quake4 for hours and nothing happen and when I'm browsing it reboots.
Yesterday it reboot while idle, doing nothing.
It happen already in gaming, but I restart, re-enter the game and nothing happen for the next couple of hours.
I think this must be the psu, because I upgraded my water cooling system and add a 3x120 external radiator with 3x120 fans plus the 120 fan inside the box.
Add to this 3 hdd, a oc GTX a oc 820D and more 1 120 front fan for the Hdds and I think my psu is having some trouble with this.
This psu was extremely cheap 45? (+/- $50).

Someone had some similar problem here?

If I start to lower the clock it gets stable @ 4.0ghz.
I dont want to buy other psu (thinking in the ocz 520 powerstream) and not solve the problem.

 

[anandtechrocks]

A new powersupply might be what you need, perhaps with a digital multimeter you could test the stability and consistency of your current power supply's rails.