troubles with sudo/root

I have an old computer with a Samsung as it's primary hard drive. it's running Xubuntu Feisty Fawn, and just now today getting back from camping every time I put in the root password it tells me that it's incorrect. I'm suspecting that there was some disk error and that the passwords stored hash+salt has been corrupted; but my two questions are:

a) is simple random disk error really a probable culprit?
b) how do I fix it?