Newly built computer won't turn on, what is wrong?

I have only tried turning it on with the motherboard placed in the cabinet.

here's some tutorials => https://www.youtube.com/results?search_query=how+to+bench+test+a+motherboard
Why guess?
Digger

I'll see if I can try one of these bench testes once I get the time and return with the result. But as far as I know my motherboard doesn't have a powerbutton on the board itself like in these videos..

at other videos. No power button is needed. You short out the pins on the motherboard very quickly with a small screwdriver
Here's how one of my bench tests looked=> http://i1365.photobucket.com/albums/r744/itsdigger/2013-12-27_12-31-02_zps80a60850.jpg?t=1401294365
Digger

I'll see if can manage to do a bench test tomorrow. I'll post the results when it's done

and look for the Pos. and Neg. power pins to short out for bench testing they say PWR I believe.
Let us know how it turns out....
Digger

I removed the CPU and the about 5 of the pins on the motherboard where the CPU connects is slightly bent. Should I try to straighten them out or do I need to get a new motherboard?

You probably got a returned board. Most of us want a PC to last years. This area is key to reliability so get a good one.
Bob

at that processor too, If aything's smashed or bent , you'll have one heck of a time straightening that out. I don't even know if you can.

Digger

The CPU looks good. No visible signs of damage atleast. there is no pins on the CPU itself but these golden surfaces instead. I guess the pins are on my motherboard instead, wich is what got damaged.

I have heard that CPU's can be very fragile and that you can break them by touching the backside. I guess this is because of a lot of CPU's got pins there? So accidentaly touching the backside of my CPU where the small golden plates are should not be such a big deal right? cuz I can't guarantee that I havn't accidentaly thouch those plates just a little bit. the last thing I want to happen now is to find out that the CPU might be broken because I slightly touched the golden plates after spending a lot of money on a new motherboard.

again, there is no visible damage on it.

.... probably the 754 processor by AMD. Since then "pins" have often been little better than a "hair" for durability. Still, it's easier to straighten bent pins on the current AMD processors using a couple toothpicks slid in cross rows, or with edge of a credit card, than it is to fix bent pins that are on the motherboard itself. Even then one has to be careful when trying to fit into the socket AM2-AM3+ motherboards.

If the pin isn't actually broken, but bent over, you might can use a coffee stirrer cut in half lengthwise to slip over the pin and bend it back up to something resembling straight.

I don't like the way Intel does theirs.