Blue screen--C0021A

[Gamist]

Hello all

Nowmy friend told me his computer occured this problem:
Today he opened the computer as normal,but couldn't log in.
Before welcome screen,he found the screen become blue and shows like follow:
C0021A unknown hard Error .

After this ,he restart the computer several times but no successful.Couldn't log in with safely system.
Can anybody help me to solve this problem?
Thank you very much.

[Gamist]

BTW,his system is Windows XP