microsoft security updates

[pace59]

Help, please. The automatic updates were done on a client pc with o/s xp. The person can log into their p/c with their id that they have been using for quite awhile. However, they cannot log into any shared network drives. They get an error that they need to enter their user name and password for the network. This has only started happening since he got about 15 automatic security updates from microsoft. It is not a network issue most likely as he is able to access the internet and did have email access but now he has the error to enter his password. THe problem is too that the password that he is using to log into the p/c with will not work on this error, nor will an older password. If another user was to log onto this guys p/c they have no problem once they enter their password that they had previous to their current one into the error message as listed above. It is the main user of the p/c that cannot
access anything on the network.
Can someone please help? The guy cannot work and I dont want to replace his p/c by wiping it out and starting over. I have checked the firewall and dont see anything blocking it but I don't really know what i need to check there.