I wonder if the problem is overheating or an erratic power supply box?

These are the render settings I used for a recent mesh-lit scene:

I don't want to limit the maximum bounces; Superfly will only use as many bounces as needed to complete a raytrace. Setting clamp direct/indirect samples to zero removes the clamping. I don't actually wait for 210 pixel samples to complete; when the render cleans up (graininess disappears), I cancel the render and export the image.

Yes, I'm offering to give you processors (four? enough for two dual-CPU workstations?); I understand your budget constraint. I don't need them (these were pulled from my servers/workstations when I upgraded the blades to X5675 and the workstations to X5690) and they would give you a boost toward a rendering workstation. You'd need to either scrounge a dual-CPU motherboard (1366 CPU sockets), or better, buy a complete used workstation which has a motherboard with dual 1366 sockets. Here in the US, eBay is a good place to find used enterprise-grade computers. The used workstation can have lesser CPUs installed, or only have one CPU installed (or none). I'd get one which already has plenty of RAM installed. Replace any used hard drives, and get an OEM Windows license. I don't know if a packet with processors will make it past Brazilian customs without a big tax charge.

Poser 12, in feet.  

OSes:  Win7Prox64, Win7Ultx64

Silo Pro 2.5.6 64bit, Vue Infinite 2014.7, Genetica 4.0 Studio, UV Mapper Pro, UV Layout Pro, PhotoImpact X3, GIF Animator 5