BSD..????

I’m running WinNT4.0 Wrkstation with Sp 6..
Just got a error message..
Stop: c0000221 Unknown Hard Error
\systemroot\system32\ntdll.dll..

Is this Hardware error or software error?
This HD has been reimaged before and was working fine until now…Haven’t changed any settings or installed any new program..

I’m thinking this is HD issue…
Please help..

Thank you all..