my guess is driver problems ,possibly corrupted during install , I have windows 7 ,on 3 machines including Ultimate 64bit ,home premium 32bit and UltimateN in 32bit and every reader , (4) external drive ,printer camera ,etc. are all recognised (and correctly displayed)
I would check the usb section in device manager , and if nessesary uninstall the usb drivers ,windows will reinstall the correct ones on restart automatically .
you say windows is not showing them ,do you mean (in explorer) via my computer . or are they simply not triggering autorun.
if windows is not showing them try another usb port ,on the back instead of front . as a last resort you could run the windows 7 installation disc and choose repair option.