Hi, A bit of history: I've been experiencing blue screens of death for over three months now. It all started when I installed an old ATI HD 4850 video card in a new computer and installed the related catalyst control center software/driver package. Over time after that install, I began to experience blue screens of death while playing certain games, such as League of Legends and Minecraft. It was occasional, and not too problematic, but as time went on they became more frequent. They would refer to the atikmpag.dll and atikmdag.dll files which are part of the Catalyst package, and upon researching a little further I found that these files were often responsible for causing BSOD's on otherwise problem free computers. To make sure it wasn't memory related, rather than video card related, I ran memtest 86 multiple times. Each time I ran it (and left it overnight) it came up clean. I ran chkdsk /r a few times, also, and performed OS repairs to try to resolve the problem. Each time the problem would lessen temporarily, but then come back. As the BSOD's continued, I noticed they started to refer to the ntkrnlpa.exe file, but I brushed this aside, expecting this to be caused by the card also. In the end, believing the problem to be solely caused by the video card I purchased a new video card, this time an nVidia GTX550 Ti, formatted the drive, and started over. This was a few days ago. Two days after, starting yesterday, I've started to get BSOD's again. They are just as frequent and problematic as before, except now they refer to ntkrnlpa.exe, halmacpi.dll and kdcom.dll. The bug strings I've been getting include 'KERNAL_MODE_EXCEPTION_NOT_HANDLED' with the code 8e; 'IRQL_NOT_LESS_THAN_EQUAL' with the error code 0a; 'BAD_POOL_CALLER' with the code c2, and the latest one 'DRIVER_CORRUPTED_EXPOOL' (c5). Every BSOD references these three files. I've run memtest more times than I can count, each time it comes up clean. Every computer component is new (~6 months), except for an older non-system hard drive which is rarely used for anything. The OS is sparkling fresh, I haven't downloaded anything except League of Legends (thus removing viruses/spyware from the equation), all drivers are current, but the BSOD's continue. I've also run a full burn-in test, and that was clean, also. What on earth could be causing it?