Question : Problem: PS2 mouse & keyboard and also USB ports not working - no power

Hi I have a customers desktop - its ports suddenly stopped working
PS2 Mouse & Keyboard are not detected
I tried USB mouse and keyboard - but usb ports appear dead -  memory sticks not detected , no light on mouse, keyboards  etc
I pulled the bios battery to reset and now it says "checksum default loaded press F1", but when i pres F1 nothing happens cause the keyboard is not detected
before i removed the bios battery it actually booted up to xp with no errors , but could do anything as no keyboard or mouse. did not detect usb hardware plugged into it
Case was not unplugged or moved before this problem occured
I also noticed sometimes the power button needs a couple of presses to get going - not sure if this is related
This is weird , please help!

Answer : Problem: PS2 mouse & keyboard and also USB ports not working - no power

note that bad caps can be in the PSU also !
anyway here my recepy :
i suggest testing with the minimum setup - disconnect also all peripherals and network cables :
motherboard + cpu + 1 ram stick, video card, power supply
on boot, do you have a display?
if NO it is one of the connected, swap ram, Power supply, video card - leaving only motherboard and cpu
if Yes, add devices till the problem shows