Get the memory card out of your R4 adaptor, putt it into a card reader.
Connect the card reader to your pc and goto Start/run.
Run this command: chkdsk /x /f /r x:
Putt for "x:" the drive letter where your card reader is at.
If the file system is repaired download the newest R4 Kernel and unpack it to your memory card, use 7zip, this software is free
and handles zip and rar files + many other types.
Use safe removal to disconnect your card reader, so that the file system at the memory
card wont get damaged.
If this wont work, you'll have to format your memory card using fat32 and unpack afterwards
the kernel files to the memory card.
To format goto start/run and use this command: Format x:
"x:" Is again the drive letter where your card reader is at.