USB Drives not detected after reboot

Hi folks

I'm running two WD external USB storage drives. Anytime my W7 OS reboots, I have to pull and re-insert the USB connections to make them available.
What am I not remembering here?
Thanks for any replies.

Did this start all of a sudden?

Have you installed OEM drivers for mobo/chipset and USB from your comp's manufacturer (or that of your board)?

Do you unmount the drive before rebooting/shutting down (using the "safely remove" command on the tray icon)?

Also, if you load device manager and rescan for hardware changes (last icon on the row), do your drives get detected again (without the need to unplug/reinstart)?