Hello Kio - welcome to the forum!

Personally I think if your graphics card requires 500 watts and your PSU is 575 watts, ideally you could do with a more powerful PSU - its always better to have more than you need

Anyway thats my two cents worth

I have opened your thread so one of our great techs or helpful members can provide some suggestions for you

Regards,

Smokeycheech

hello kio
I believe all three staying on signifies a critical core power fault. One light is temeprature, the other two are the respective power plug being lose. All three means not enough power. i would say with all the hardware you have in the computer that you need a much larger psu

Sigh... the GPU was kind of a budget stretch, oh well.. It does work ok now, I guess it doesnt like when there is too much load on it. I guess the problem comes from current, not wattage as such. The second hard drive is not too active, since its an archive, and i dont use the optical drives at all, so they cant put too much load on the system.
I have just been looking at this PSU:
Antec EarthWatts 650W PSU - 80Plus Certified 12cm Fan 3x 12V Rails - Ebuyer
Reviewers claim it has 25A pci-e rails, while mine only has 16 at max. Do you think this one should be enough to compensate for the hungry ATi?
I still have no idea why it doesnt poweroff properly - keeps stuff spinning and glowing, another thing - since i installed Win7 it sometimes makes sounds similar to a power cut off, but the system keeps working and nothing even shows a sign of such a thing. I.e. browsing the Internet and u hear quite a loud "crack" as if an old-fashioned switch has been turned, then there is a distinct sound of a discharging capacitor - "Ssssiuuuuit" and thats it - internet is fine, windows is fine, not even a flicker or a glitch. In the good old days, it used to make such sounds on system poweroff.

Thanks for the advice guys.

EDIT:
By the way, I just looked at my current PSU specs again - it has 2 12V outputs - one for 18A and another for 16A. The PSU only has one Pci-E power connector, so I am getting the other power source from an adapter from 2 4-pins. I just thought i might be getting the second pci-e from a 16A rail, so a total of 34A, while a similar GPU from Nvidia - GTX260 asks for a 35A power supply. So it works, but "just". What do you think?

i would personally say get as big as you can afford , as the system will only take as much as it needs to run, from what i have read that gpu is power hungry so you need something that will keep it fed,
the prob with your current psu could be down to a faulty switching unit failing to completely shut down ,how old is it ?

It is about 4 years old, I guess. Jeantech 600, i think this is its full specs,if you want:
Jeantech Online
It does have a big Pentium 4 sticker on it, so 4 years or so for sure.
But, it doesnt simply not shut down. I made a few observations, when I was really trying to find out whats going on.
When i shut down Windows and it all remains spinning and glowing, I switch the power switch on the back of the PSU to off, it all, of course, powers down. Then, if i switch it back on within a certain time - up to a few minutes or maybe even up to an hour - it starts spinning again like before i switched it off.
BUT, if i switch it off and let it stay there overnight, next morning when i switch it back on - it doesnt start spinning. Occassionally, on turning the ON switch - the fans get a little jerk and thats it. So i can then switch the PC on and when i switch it off - it remains spinning anyway. This fact of the fan jerk when supply gets power makes me think of a faulty motherboard power management. I am not very knowledgeable in this area, but i think fans do not spin because the supply has power, but because motherboard gives them power.
One close problem to mine I saw on the internet had an answer suggesting that Motherboard thinks the system is still too hot to switch fans off, so it lets them cool it down. But I do not remember the fans to stop spinning at some point after poweroff and also all of the system temperatures are well within normal.

from your description it sounds like its time for a new psu ,
when running a psu provides power through the system to all fans ,(unless your running something like a thermaltake system) if they fail to shut down when you tell it to then there is a fault with it