What is your OS? And, if it is XP, do you have SP2 installed? If not, install it.
Advise from ASUS about USB problems is:
Step1 : Please update to latest BIOS.
Step2 : Please enter BIOS by pressing F2 at start up and go to Advanced -> Chipset -> Southbridge to see whether the option of USB 1.1 OHCI Controllers and USB 2.0 EHCI Controllers are set "enabled" (only applicable for some models)
Latest BIOS for your laptop can be found
here by searching on model A6U and BIOS.