well, I turned my PC and my monitor said that "Please check the signal cable" I thought the D-sub cable was loosed but i've tigthened it but it still say the same. I've checked my vga card and it's ok no error. Can anyone help me to solve this problem?
Try re-seating the video card. Sometimes the spring contacts don't behave. I had that happen before-- but I did hear a beep code. Completely power off the system first (not just ATX soft off, flip the power switch or unplug the power cable) before re-seating.
Do you have a good power supply? Were you doing any overclocking of the AGP slot?