[Skybird]

Thanks to all.

However, you cannot explain why the system so far is stable when being under full working load, both CPU and graphics card. It should be then when too instabile power supply shows the most obvious, since then the demand is the highest, CPU, graphics, RAM, and sound.

I now have the symptom - currently the only one - that when I started the system yesterdy and today morning, the LED indicating HD activity is on for 1.5 - 2 minutes, while the screen remains pitchblack and nothing happens, the monitor even switches back to standby mode. Then, all of a sudden, booting begins, monitor goes on, with the Windows loading screen, without displaying the usual BIOS screens. When I switch off immediately after that, and try to reboot, it is the same. However, when the system has run let'S say an hour or so, for longer time, and components are a bit warm, rebooting is done in the usual way, and reliable, and fast. Booting a really cold system= long time, rebooting a warm system (including power switchoff)= short loading time. I also have an old graphics board inserted now, which ran fine since 1.5 years, and before that in an older system. So far no effect from that change. I will put the new card back in, and run it and the fan with a separate AC from an old system for some days.

but somehow I have a feeling now that it neither is overheating, nor power supply. I just came back from town minutes agho, and have asked in the store where I bought the components and let them built the tower. The guys there are both freindly and good on their matter. They said that due to the circumstances of having a stable system even when maximum instability should be expected (full working load), the AC probably is not the problem (as long as it has no erratically appearing problem with broken internal hardware). And according to my description of how the system it set up (open, ventilator), overheating would be a surprise to be the cause of problems. Remains: motherboard problem, RAM problem, HD problem, soundcard problem (the latter I do not take seriously into account).

My tip is the harddrive now, the thing was very hot two days ago (it used to be cold, since it get's it'S share from the ventilator, and directly), at one, as described somewhere above. I could imagine that it received some kind of damage from that. But overall heat problems I cannot imagine to be the source of problems, the tower simply is too open and receives too much fresh air from a separate ventilator.
Will exchange the HD sometime this weekend, and let the system running all day for the time being.

I have no battery backup. the talk above was only about that small Lithium cell that motherboards are used to be equipped with. We also have absolutely stable power lines over here, no blinking, no blackouts or brownouts, nothing.

Never have built a system by hand myself, only decided on components, and let other do it. I can chnage a sound or graphics board or RAM bars, but a motherboard and all cables and AC - still quite impresses me.

Assuming I try a new AC - and I will not invest that money as long as it is not safe to say it is the AC causing the problem - could I trust in that if connecting connectors really matches by form, that the according device really gets the voltage and ampere it needs, then? Or do different power supplies in those many cables of a AC nevertheless sometimes have the same plugs?