I want to make low energy PC
Silent as possible.
Office programms internet browsing, must be p[ossible to watch some decent video online,no gaming.

Ideal would be to make the case without fans, but I am not sure if this is possible with this components.
What would be the most silent solution without overheating danger?

Can I use a passive PSU without any casefans and/or is it neccesary to plave a fan in the back of the case?

These are components:
Case Lian Li PC-Q03B
Mainboard Asus C60M1-I
Kingston ValueRAM KVR1333D3N9K2/8G
Samsung 830 series 128GB
DVD Slim drive SN208BB

Asus typically doesn't make the most efficient or coolest-running fanless boards.
And this case isn't ideal for fanless cooling (no venting holes on top).
But it would probably be OK not to use fan... hot, but OK. If you want to be safe, ask Asus! They know how heat-tolerant their board is. We don't. Maybe they've explained this in the documentation actually.

I've been waiting for a board such as this one to show up (though I would rather use an MSI board) last year. It's a bit late now but it can still be useful for NAS builders.
It's a bit slow for a desktop though. Some people will be OK with that but others would hate to use such a desktop. Your ability to play online videos is going to depend on the software and resolution.
You're wasting your money on the SSD and RAM anyway. With such a board, it doesn't make sense to buy more than 64G and 4G.

The Asus C60M1-I is definitely an interesting board. Though I suspect it isn't the most engery efficient as it uses an Integrated ATI Radeon HD 6290 GPU.

Most computers spend the vast majority of their time at idle. At idle, all the modern Intel CPUs, including even the 4 core ones idle at about 4 watts. The main difference is what happens when you put a load on them. The CPUs step up to the load, but then absorb wattage in order to do the work. On a work done per watt, the larger CPUs tend to be more efficient than the smaller ones.

If you look around at al the bench tests, you will see that Intel motherboards tend to be the most energy efficient of all the brands... often my more than a little. I would start with an Intel board if that is your priority.

Take a look at the Intel 2105 or 2125. They have the 3000 integrated graphics that will handle more than what you need... and do so while sipping electricity. They are dual core CPUs (that will make you feel better than having 4 cores)

Couple that with an energy sipping Intel motherboard, you will probably use less energy than your original configuration, with much more horsepower. Something that will carry you through more generations of Windows.

Using a fan isn't necessary, but it is well advised. The initial slight wiff of air from even a 500 rpm fan makes a big difference. And you won't ever hear it unless you live in an anechoic chamber... and maybe not even then.

The case you have selected has almost no ventilation. That coupled with no fans is just asking for trouble. If you want no fans, this is a much better case:
http://www.techpowerup.com/reviews/LianLi/PC-T1R/

Slipstream makes some nice 500rpm fans. Why not go with more conventional cooling, but use those 500rpm fans. You won't hear a thing... and they use almost no electricity. They are nothing.

There is something to be said for the Seasonic PSUs with a fan. The fan doesn't kick in unless you hit a 20% load. The only time that fan will move, is if you need it, and then you will want it moving.

It's nettop guts. In a PC enclosure

If all you want to do is surf the web and watch online videos, it'll do. Here's an Acer nettop review at notebookcheck.net. Acer's implentation uses ~10W under load. Yours will be higher, but not by a lot. The peripherals will drive it. Downside to the Asus board is no HDMI (if you wanted to use a TV for viewing). For efficiency, you ought to look at using a PicoPSU + power brick rather than an ATX PSU.

I would tend to agree the super small pc's net tops if you want to call them that will be quite decent enough for office, web and watching a bit of video.
For a normal pc whilst the Intel Core i3 2105 is a nice low energy use CPU, it's overpriced for what you get.

I don't know if a Scythe Kozuti would be too wide for the DH61AG, but if it fits, a Kozuti

http://www.newegg.com/Product/Product.a ... 6835185167

with the DH61AG case/PSU/mobo kit

http://www.mini-box.com/KIT-M350-INTEL-DH61AG-19V-160W

with an Intel dual-core Sandy Bridge chip and an SSD like the 64 GB m4:

http://www.newegg.com/Product/Product.a ... 6820148524

would be a nice quiet system, with only one fan. I asked, and the DH61AG boards that mini-box had at that time were too old to support Ivy Bridge CPUs.

Thanks for help.
I decided to go for Zotac ZBOX Nano XS AD11 Plus.