BSOD - BC Code 7f, ntoskrnl.exe

Sorry to ask for help on a first post especially when I'm going to struggle to return the help.

I've got a Dell XPS L501X Laptop bought at the start of 2011. It's running Windows 7 64 bit as pre-installed by Dell. The blue screening is set to "reboot and pretend nothing happened" mode and I've been noticing it over the last 3 months. If I'm around when it reboots I can see the error report that pops up - always it says BC Code 7f. Below are screenshots of one of them. Documents.zip has the files suggested in the sticky post.

I've read through similar posts on this forum and have got so far - Blue screen view shows ntoskrnl.exe as the thing that's crashing. Memory gets suggested a lot so I've run memtest86 (only did 2 runs) but everything seems OK.

Any advice much appreciated. I'm under guarantee but would be keen to be properly prepared before phoning Dell support.

Just did it again. It's not actually blue screening - just powering off suddenly and then saying it wasn't properly shut down when it restarts. That doesn't leave a dump file.

I'm guessing a power issue. Though it's a laptop and has a battery so shouldn't be affected by trouble with the mains supply.

Searched around here a lot more - the regular (every day) crash is not a BSOD, it's a sudden shut down. On start up windows says it wasn't shut down properly etc. Of course there is a BSOD every month too. Read around and understand the sudden crash is tricky to diagnose because it leaves no error messages.

Bought some new ram just in case. Still crashes. But at least I've got an extra 2Gb now.

Tried realtemp and the CPU is running at 50C-55C most of the time, so not that.

Will keep you all posted.