While booting my desktop, I found there was no beep, no screen with little disk noise. In the first place, I thought it was the video card, so I uninstalled and cleaned it, I even refreshed the gold fingers by an eraser. Then, I re-installed the video card. But it's useless. Now what?
If OS was started, it should have lots of noise during booting and I can ping the computer from other computers afterwards, but it was quiet and unreachable. So I changed my mind, and paid attention to cpu and memory, but which comes first to be checked? Generally, cpu is reliable, so I decided to check memory modules, they looks a little dusty, so I uninstalled and cleaned them, then installed them on the motherboard, ensured they were installed well.
When everything looked fine, I reboot my desktop. It succeeded with one beep leading. Now, we have the conclusions: The failure was sourced from loose contact of memory modules.