Windows keep rebooting without warning

I assume that should read you changed your case, not casing? Anyhow, it could be a short. Did you use all the standoffs and/or paper washers that came with your case? Anyhow, give the board a good once over. make sure all connections are snug and that all standoffs and washers (if needed) are in place.

Yea I will try that..Now I have confirmed that it is definitely hardware problems as it now shutdowns nearly right after I switched on the computer..

Yea I used all the given accessories from the case

Have tried without my GPU on

To eliminate the case as the problem, remove the board and set it on top a piece of cardboard. Keep all components connected and start the system with the board out of the case. If it works fine, then you didn't have the board properly mounted in the case.

Other things that can cause immediate shutdown are the PSU and an overheating CPU.

Ok...Tested on cardboard
1st try: Didn't reboot after sometime so I decided to try it with my GPU on
2nd try:With GPU, reboots
3rd try: Plug off the reset cable, system does not turn on and off.. Nothing displays on the monitor however it showed green stuff for a few second

Sounds like a GPU failing here and reset cable shorting out constantly?

Minimum hardware to boot (at least into bios) is cpu, ram, and video card so it makes sense it wouldn't boot without it. In fact, if your mobo speaker was hooked up you'd probably get a long beep to let you know that no video was available.

I'm not sure what's up with the reset cable. I've never tried booting with it pulled off but I don't see why that would be an issue. Normally, you just temporarily short the reset wires to get a reboot. So, with the reset button hooked up and video card installed, does it stay on? You said 2nd try worked so I assume that's a yes. If that's the case, the motherboard may have been shorted out against the case. Leave it running on the cardboard for a while to be sure it will stay on. If it seems ok, remount the board in the case and see what happens.

With the reset cable plugged, it stills turns on and off.

Now the mainboard is back to the case now and I tried running it again without the reset cable
It gives a standard 1 beep. The monitor does receives the signal but the screen does not shows anything and seems to flicker occasionally and show green screens

This kind of puzzles me as the GPU did not show any signs of failure recently
Maybe because of cheaper brands? It was a Leadtek

That sounds like the video card's ram is defective. I've never known this to cause a computer to shut down, only have the video artifact or show wavy lines. Also, I've had a couple leadtek cards in the past and they ran extremely well and lasted a long time. Of course that doesn't mean you won't get the occasional dud.

If you have a spare vid card and/or PSU, try swapping them out. How long have you used this system before moving it to a new case? I assume it was all working normally before the move?

Doesn't have a spare PSU or vid card  

Used around 3 months in the old case

Video card shutting down the computer is entirely new to me as well..though I somehow have the feeling that the constant on and offs might have cause the graphic card to die..>.<

Yea I also have heard Leadtek is quite a good brand actually

I'll have the GT430 tested soon

Thanks for the help  

When you moved the mobo did you by chance accidently loosen the cpu's heatsink? I see you listed your CPU temp, but was that before or after the move? If the heatsink has come loose the CPU will heat up quickly and it's thermal protection will kick in and shut down the system.

Nope, I'm using CM N520 so I can't imagine it getting loose anyway and seems to be working fine after I moved the mobo as well