Check computer's domain account, if it is still valid. If it is not, then
disjoin PC from domain, reboot and add PC back to domain.
Before you disjoin PC from domain you should check if you know the password
for local administrator on PC. You will need this account once you disjoin
PC from domain and reboot PC. Without this account you won't be able to
log-on to PC once it is not in domain also meaning that you won't be able to
add it back to domain.
Mike