Replaced power supply, USB mouse/keyboard non-responsive

Hello -

My computer was suddenly not powering on. I replaced the power supply, and the computer booted up, albeit with 1 short beep followed by 3 short beeps at POST. I'm not sure what BIOS it is, but it is a 3-ish year old Asus motherboard.

The problem now is - it will boot to the Win XP login prompt, however it is completely unresponsive to my USB keyboard and mouse. Oddly, I believe it is providing USB power because I have another peripheral (USB MIDI synthesizer) hooked up that powers up just fine.

I tried pulling 3V CMOS battery, different USB mice/keyboards etc, no luck. Any ideas why the USB mouse/keyboard are not working after replacing PSU?

thanks!

While in login screen , try to un-plug then replug in usb devices, if not try to plug the usb devices into different usb ports if possible.

Have tried that, still no luck.

Also unseated/reseated RAM etc to see if bad RAM was the cause. Still no luck.