Been having these crashes for a while now. They don't happen that often, but they are frustrating none the less.
A little back story, this is my first build. Have it for about a year and a half. Initially I had random crashes but only when playing two particular games L4D and GTA IV. I figured out that it was a problem with one of my sticks of ram, so I removed it. That seemed to fix my problems. Back then I had a dual boot XP and Vista. I continued with the single stick of ram, upgrading to Win 7 Beta, RC and eventually the retail release.
After my last upgrade I began experiencing the ntoskrnl.exe crashes. My system is overclocked but I began experiencing the crashes prior to the overclock. I also added the previously thought faulty stick of ram.
Since I began experiencing the crashes I've tried quite a few things. I ran Memtestx86 on both stick together and separately, last test ran for 9:30hrs no errors with both sticks. Undid the overclock, ran Prime95, Intel Burn Test, all passed. Reinstalled all my drivers. Even did a complete reinstall, more than once, but to no avail.
The only thing that I'm certain of is that the crashes happen when ever I play Youtube videos, or any type of embedded flash video. Not all the time but every once in a while I'll be watching a video and bang BSOD. It's also happened when watching a regular video file, mp4 recorded from my phone, but that produced a different crash.