Code 51 refers to a POST message that tells you the BIOS was not able to allocate the required ressources to the PCI bus.
I think it means in your case that when your card reader is plugged, the BIOS tries to assign the ressources at boot time to it and fails. (that is before it even tries or not booting to it). What you can try is:
- Reseting your BIOS settings. (in order to get the default config).
- Try disabling some unneeded devices in the BIOS (yeah... I know, it could be hard...)
- Maybe it is because of an incompatibility with your card reader and the BIOS...
- Did you manually configured the BIOS to assign some ressources?
Hope this helps.
I have seen this behavior on different Intel platform models, Also, if I remove the USB drive, few seconds after the mobo boots correctly. Do you see the same?