Bsod error

I hope I am doing right but I thought that now my problem had changed from what I thought was a failed hard drive to a something elsie, I sqhould ask a new question. I apologise if I am wrong.

The hard drive had been taken over by viruses and after using bitdefender, all the viruses were gone and when I rebooted I got as far as the windows loading screen and then rebooted, I went into F8 and disabled the reboot sequence and this time got a stop error code C000021a at OXC0000034, I have checked the memory modules and they are ok. Please let me know what the cure for this is, thank you