I have a failing HDD in my second PC that gives the same blue screen error (IRQL_NOT_LESS_OR_EQUAL) randomly. It takes ages to get started up. I'm going to have to replace it, which is no big deal as it's pretty old anyway, and doesn't start up or starts up after a long delay at boot sometimes. Yesterday I had a failure of lsass.exe, at boot, and the system shut down. Usually this type of shut down is initiated by "NT_AUTHORITY\SYSTEM" on this occasion it was just "\".