Just to clarify: you are using the USB ports on the motherboard itself i.e. the rear of the computer case?
There was a new BIOS issued for that board about 3 weeks ago:
http://support.asus.com/download/dow...Language=en-us
Insert: motherboard > socket 775 > P5LD2
This would not explain why it used to work and now does not but it is another option to try.
If you are unfamiliar with flashing a BIOS please read all the "Read Me's" and ask here if you have further questions.
I, myself, am out for the night but will return tomorrow.