mobo: MSI K8N NEO4-F
cpu: AMD Athlon 64
keyboard/mouse: Logitech Internet Desktop Pro Black (PS/2)

Im building a new computer and assembling all the new stuffs that i brought. Everything works fine, except the keyboard and mouse issue. Here's the problem

After a couple of secs or minutes, depending how long the system have been shutdown. The keyboard and mouse freezes. Even in BIOS i notice the keyboard will freezes in secs. or minutes. And sometimes it can't even detect the keyboard at all at start-up.

My conclusions is that its kinda grounded, i disassembled everything and layed out the motherboard on a cardboard attached all the wires and everything that is needed... System went fine, i even waited like 30mins run 3dmark and problem never occured again. But at a time i put all things back together inside the casing, the same problem occured again.

How come it still works using USB keyboard/mouse, i already tried it.
-Can it be grounded to the casing?
-At first i thought problem is the motherboard itself,
but how come it work fine when i layed it all without the case?
-Can the fron panel I/O connectors be responsible?
-Is the plate that comes with the motherboard to be attached
in the casing can be grounded?

Hope you can help me guys.

Is the plate that comes with the motherboard to be attached in the casing can be grounded?Please describe the plate, and its exact function.
Also, if it's not required, then install the MB without the plate.

If that does not work and the standoffs(support posts under the MB) are made of metal, then make sure that the standoffs are installed only where there are MB holes.
If that's ok, then make paper washers from a manila folder, and install them between the standoffs/screws and the MB.

sorry to misunderstand about the plates. it's actually called I/O Connector Port Holes or I/O Template(s), attached image in this post. I will try soon about not putting this templates on the casing. and about the standoffs, yes it is installed on the motherboard holes in bronze-like color, does standoffs conduct electricity? and also thanks for the manila folder advise i will try them too, was kinda suprised when you said manila folder never knew they were called that way, as i am living in the phillippines :D. Still to busy in work and dont have time when i get home. But thanks for the reply, i will keep you guys updated.

Yep, bronze or brass standoffs are part copper, which is an excellent conductor of electricity.

do you recommend to use them as standoffs? cause everything was just fine when i layed it on the cardboard, ill try to the surgery again tomorrow cause its weekend, and ill have time when i get home. ill just inform you again. thanks

Okay i've done the pc surgery again, remove all the things inside the casing and layed it all on the cardboard, this time it gotten worst. keyboard and mouse won't detect at all. so i decided to blame the motherboard and went to the computer shop where i brought it. i got the motherboard with memory & processor attached, videocard, and the harddisk.... only to find out that everything was working well, including the PS/2 port! now what did i missed? now i'm blaming the power supply, cause its the only thing that were left and untested. as i'm typing this post now, im using my Logitec Internet Pro Desktop Black, Keyboard & Mouse PS/2 in the office with no problems at all!

There's nothing left to be blame but the power supply...Is it possible for it
to cause such erratic/unstable PS/2 port connection? I also notice it once
while im testing, after the keyboard and mouse hanged up, i heard a tiny clicking inside the PSU then the entire system
shut down itself, but i didn't mind that. This is a generic 450 watts that is included in the casing that i brought. So what do you think guys?

Clicking inside the power supply indicates a possible problem with it.

So What do you think are the problem?

I have the same problem, when i connect my ps2 mouse its working but after a minute theres a click noise and my keyboard led are flashing, after that my keyboard became malfunction.

my cpu casing are grounded, what do you thing are the possible cause, do you solve yours?