[igalan]

I have no experience with Soltek, so I can't tell you. But the Intel 865PE chipset that it uses is very reliable.

About the CPU thermal paste, it's very important to have proper contact between CPU and heatsink. For this purpose there must be thermal paste in between. Apply a very thin layer of thermal paste over the CPU only, almost transparent, evenly. If you're using some special compound, follow instructions, as some require a different application. A badly placed heatsink can cause the CPU to over heat and slowdown or even shutdown. But you said that temp was stable at about 40ºC so that doesn't seem to be the problem.