tech support

i am not able to revert back after upgrading the IOS in CISCO 1751 router, which stopped detecting the serial & FXS cards. Thisis what i get after erasing the flash and installing the IOS.
Router#sh flash
^
% Invalid input detected at ‘^’ marker.

Router#sh flash:
^
% Invalid input detected at ‘^’ marker.

Router#dir
%Error parsing (Bad file number)

Regards
Chandramouli