Mac Pro (early 2008) keyboard stops working

My Mac Pro (early 2008) has the Apple USB extended keyboard go no ops after the computer has been on for a while. This has been happening for quite a while and began shortly after I installed 10.6. It seemed to disappear for a while after 10.6.6 showed up but has returned since 10.6.8 has arrived. It seems to happen only when the computer goes to sleep but it does not happen every time. But it does happen most times. It appears that all USB ports on the back of my Apple monitor become unusable when this happens.

Anyone have any ideas? This has the feel of the sleep issue this model had with an early OS a few years ago.

MacPro3,1, 10.6.8, 32 GB RAM, dual 32 GHz quad-core Xeon chips, 4 bays populated, 1 TB, 2 TB, 2 TB, 2 TB