Was it working ok, then stopped working? Or have you just installed and it has been like this from the start? Are you running in a VM or bare metal (or something /somewhere else)? If VM, what type (VMware/VBox/OVZ/Xen/etc)?

Posting your dmesg log (/var/log/dmesg) might be useful (although to be honest unless it's something straight forward I'm not sure how much help I can be...)