No video, No keyboard, no usb, no bios

Hi all,
Since last week my computer was playing strange. It restarts couple of times to start Win 7. But Yesterday it couldn't start & keep restarting. I couldn't get video & Bios. It is 1 & half year old and was working fine. we haven't changed a thing in it.

Motherboard MSI G31 V2 MS-7529 VER 1.1
Processor Core 2 Duo
Kingston DDR2 2gb Memory stick

What I did..
1. Turned PC OFF, removed all HHD, DVD, RAM, PCIe Video card, Keyboard, mouse, video all except processor, cleared cmos removed cmos battery (after 30 second reinstalled battery)
when start computer it gives small beeps means varifying memory is missing, PSU fan is on, CPU fan on.

2. Installed 1 slot 2gb memory, video to integrated VGA, PS2 KB & Mouse & restarted computer now it is not giving any beep only power light on. Can't see video on monitor, mouse laser light is on, can't see KB light (No caps light - No numlock light - pressed many time) & still keep restarting the computer after 30-40 seconds. replaced KB/Mouse from PS2 to usb but can't get the light even on mouse.

Please help me as I am not able to identify the problem. I tried video on PCIe with 6 pin power but still can't get video. Fan on Video card starts but noting on monitor. even reseated memory & cpu but still no difference to above situation.

Appreciate your help on this.

Thanks & Regards,
Manish


UPDATE:
Just bought new PSU & tested still same result. re-seated Mother board, CPU memory, PCIe card.

now only experienced POST & BIOS technical person can pinpoint the problem.

I tried below setups to check but all gave same result all fan works but computer restarting, no beep & no video output results.
1.CPU + memory
2.CPU + memory + PS2 mouse (mouse gives laser light)
3.CPU + memory + video (No video on monitor)
4.CPU + memory + PS2 mouse (mouse gives laser light) + PS2 KB (no keyboard caps / numkey lights)
5.CPU + memory + PS2 mouse (mouse gives laser light) + PS2 KB (no keyboard caps / numkey lights) + video (no video on monitor)

Above tried with different PSUs, memory sticks & integrated/PCIe card videos, clearing CMOS / removing battery (Battery voltage is 3.17)

But Still no luck. does it means BIOS is currept OR something else?

Thanks
Manish