Check any Bios setting for swithed off ports, check 5V regulator supplying the USB/PS2 (usually an analogue one) and if the supply voltage for it is presesent (probably 12V). Check for short after the 5V regulator. Check any recovering fuses or any 0 ohms serial resistors in the 5V power lane for discontinuity if present. Check any switching mosfets between the regulator and USB. Check ESD surge protectors on USB data lines for shorts (very small 6 pin dual in-line devices near the USB Ports), they go short on a surge to protect the chipset and must be replaced (they are usually devices like IP4220CZ6, case type: SO6 (SOT457)).
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