External HDD Plug & Play Problem

Connected to my notebook via a powered hub are two external drives . I have it configured such that when I return from work I plug in the USB hub open my notebook lid and the external drives are immediately recognised and fire away. I have never had to reboot and it has worked well for 6 months. Then 3 days ago for no apparent reason my notebook would not display either of the drives under Start | Computer. Rebooting fixes this problem but is a pain (this takes several minutes at the moment). Curiously under the Device Manager both drives are shown and under Properties for each is displayed "This device is working properly." I have tried plugging the hub into a different USB port to no avail and I have tried plugging each drive directly into the notebook bypassing the hub. This results in the notebook recognising new hardware and successful installation but again the drive doesn't show. Any ideas on how to sort this problem out? Many thanks. pbl