Doesn't boot up

Hello,
I tried to do anything, but my computer isn't booting...
I checked the power supply, by connecting green and black wire, it worked...
Removed memory card, there was beeps...
CPU test was good...
Used eraser to memory cards, changed them in other slots, tried new memory cards...
But still nothing...
Display is blank, all coolers are working, caps lock and num lock not working... can you help me please?