Check this link on the 0c21a error;
Find the listing on the right for 21A and click it.
You may find the two links provided helpful.
I have a 866 mhz with 512 ram and an updated bios from A05 to A011. I was replacing the operating system from ME to XP Pro. After a clean install of XP Pro service pack 2 on the 20 gig hard drive it downloaded the updates and rebooted. The system then said it couldn't locate the hard drive and I did multiple reboots and checked the connections with the same results. I thought the old hard drive was the problem and put in a new 160 gig hard drive. Now, I'm getting new errors and tried multiple times to reinstall. The only new items I added were the hard drive and ram, and the bios sees both. Here is the error message below:
Stop c000021a (fatal system error)
the session manager initilization system process terminated unexpectily with a status of 0xc00026c (0x000000 0x00000
the system has been shut down.
Thanks for the help!