|"The power supply could be it... you mean that 24pin plug has to have that much? mine has 500W. It doesn't have a 24pin at all, but I asked someone experienced, that it should still run with a 20pin and he plugged in an other 4pin to sum that up. he said, that this should work. Is he right?"|
Wattage is not as important as amperage. Just telling us that you have a 500W PSU means nothing. We need to know the brand/model & amperage specs for the +3.3v, +5v & +12v rails. If you don't know, the info is on the label on the side of the PSU.
You *may* be able to use a PSU that has a 20-pin main ATX plug, but the amperage specs to have to be correct. And without the extra 4-pin, you can NOT use a PCI-e video card. The extra 4-pins on the 24-pin plug power the PCI-e slot. There's also another 4-pin plug that must be connected to the board...that plug powers the CPU. As for the light on your board, read the manual.
I suggest you remove everything from the case & start from scratch. Lay the board on the table with just the CPU w/HSF & one stick of RAM installed. Connect the monitor to the board & nothing else but the keyboard (preferrably PS/2, not USB). Plug in the power supply, switch it on, then press the red power button on the board to fire it up.