Your PSU has nothing to do with sufficient or insufficient power to USB devices. Each USB port has a limit, and the hub which powers the port has a limit in total. My guess is you exceeded it, and thta's why certain devices didn't work in the past.
However, with the new info you provided (USB mouse and KB work in BIOS and safe mode) its clearly not a USB hub lock-up.
So, try working your way through this:http://support.microsoft.com/kb/310575