Password does not work when idle-time lockout occurs

When I boot up the computer my password works just fine. I get into Vista and
my desktop loads. However, when the computer locks because of inactivity, the
system will not recognize my password. I've also not been able to use the
password reset tool for the same reason---it says I have entered an invalid
password or username. I have read here that I am not the only one seeing this
happening, but have not seen any solution posted yet. Thanks in advance for
your help.