[问题] System cannot boot

[ydj]

For a while I didn't use my old system. But today the system cannot boot,no display on monitor, no beeps. I tried different video card or power supply, no help.
What is the possible reason.
Urgent!!!

 

[大熊猫]

no beeps?确定主板通电了？CPU风扇转吗？

 

[ydj]

Yes, CPU and power supply fans work,CD-ROM and Floppy light can on/off, even a CD inside can speed up. But no beeps and display on monitor.

 

[大熊猫]

换个纽扣电池试一下。