Computer Freezes on Login

OS is Win XP SP3. When I sign on I get the message
"One of your disks needs to be checked for consistency. It then proceeds to use CHKDSK but hangs up wnen it gets to Stage 2 of 3 4% completed."
I have to kill the power to the machine and reboot. It does give me an out (I can skip the CHKDSK). However, it is a pain and I wonder if something is seriously wrong. Any help would be appreciated. Bill