Blue screen error occurs suddenly

Hello, I am using an old desktop. Performance is ok for official work. Now-a-days I found a problem which is much unknown for me. suddenly this blue screen error appears >>>
STOP 0x000000D1
I can’t work properly for this problem. I have to close my PC when this problem occurs. Recently I added an extra external 2nd hand hard disk in that pc. Now I am thinking that this problem is occurring only for this external hard disk but I am not sure actually. Now I need valuable comments. Advance thanks.
