System cannot start, no beep, no screen

Recently, I just changed the case for my system, however, after i changed the case, my system cannot startup.
Here is my problem.
When I turn on the power, the CPU fan starts up, the vga fan also starts, but there is no screen, no beep, after few seconds, the vga fan shuts down.
I tried to unplug all cards and re-install to it, no use; and I use another display card, no use.
I tried to re-install the ram, no use.
I tried to re-seat the cpu, no use.
I tried to change the power supply, no use.  
I also tried to remove the batteries on the MB for an hour, no use.
The only thing I haven't tried is to switch the CPU and motherboard.  Isn't that the problem of the CPU or motherboard?
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It sounds like you are missing the 12 volts for cpu -       normally a 4 pin plug
Usually, yes it is the mobo or cpu.
Does the whole system shutdown after 4 sec? or only the Video card fan?

If the system is started, and you hold the power switch for 8 sec, does it power off?

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But since you changed the case, i suggest to take out the motherboard, put it on a piece of plastic, or hardboard, and start it out of the case, as you may have grounded something; look for the screw positions and such
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If you are not even getting a POST, then it is usually one of five things.  RAM, Video Card, Power Supply, CPU, and/or MotherBoard.  If you have more than one stick of RAM, try each one by itself.  I would also try to test the CPU, and if that doesn't solve the problem, then you're most likely looking at a motherboard issue
Lets hope you were wearing a ESD wriststrap when putting your PC together.  Not wearing one can cause a static discharge and ruin important hardware.  Also make sure you put in all of the motherboard screws in so the mobo will be grounded to the case like nobus said.
york98Author Commented:
My system is AMD Socket A, it only has one power supply plug.

Since there is no screen, the harddisk light didn't flash, I don't know whether the system is running or not, but the CPU fan do still running, and I can see from the Thermal Panel that the CPU temperature is switching between 29-30 degree.

Yes, when I hold the pwr switch for few secs, it do turned off.

Dose your keyboard power on?
then you cpu shows some activity. i suspect the motherboard. did you try my suggestion to test it out of the case?
Chris BRetiredCommented:
<<AMD Socket A, it only has one power supply plug>> Yes, but is it a 24 pin or 20. If it is a 20, there is a square 4 pin socket on the board which must have power plugged in. If there is no plug, you have the wrong power supply.

Chris B
If the only thing you have done is change the case, then its a grounding issue.
york98Author Commented:
I finally change the MB, but it's not working again, then I changed the CPU, then it works this time.  
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