Lots of BSODs the last 10 days, frequent 0x00000109

The title is self-explainable.

The last 10 days I've been having many BSODs around the first half hour I start up my PC. After frequent BSODs, the PC seems to operate normally, until I shut it down and boot it up to experience the same issues.

Using NirSoft's BlueScreenView, I can only say that the most frequent "bug check code" is 0x00000109.
Others are 0x000000d1, 0x00000050, 0x0000003b, 0x0000000a and 0x0000004e.

So far I have only followed the BSOD posting instructions.
Thanks in advance for your support!

I used Memtest86+ V4.20 for about 12 hours.

After 10 passes with both 4GB RAM sticks on, no errors were found.

Should I test each RAM stick individually?

No errors were found after testing each RAM stick individually on slot 0.
Memtest86+ ran for 13 passes on the first stick and for 8 passes on the other one.

Something I forgot to mention on the first post:

After those frequent BSODs occur, programs that were running tend to lose their settings.
For example, Skype forgets the password (but not the user name) and uses its default settings.

I hope this will help you track down the problem.

Both internal and external hard drives passed the tests. In detail:

I've tested my Seagate Barracuda 500GB internal HDD using SeaTools for DOS v2.23.
The HDD passed SeaTools' "Long Test".

For my Toshiba StorE art 3.5" 1TB USB HDD I used SeaTools for Windows v1.2.0.6.
The reasons I used SeaTools for this HDD are the following:

1) Toshiba's Diagnostic Tool is actually a Fujitsu HDD Diagnostic Tool that doesn't recognise my HDD as a Fujitsu product.
2) The HDD's firmware report that it's a Samsung HD103SI.
3) Samsung's preferred HDD Diagnostic Tool is Seagate's SeaTools.

I used SeaTools' "Long Test" again and the HDD passed.

Finally I used Western Digital's Diagnostic Tool for my WD Elements 2TB USB HDD.
The HDD passed the "Extended Test".

I've kept the test reports in case you want me to upload them.

There seems to be no overheating during normal usage.
I wanted to stress things a little bit, though, and ran Need for Speed: Most Wanted (2012) to check the temperatures again.

The highest values with NFS:MW (on its highest settings) running on the background were:
GPU: ~80C
CPU Core 1 to 4: ~60C

I believe the problem lies elsewhere, since it almost happens during start-up.
Furthermore, I've never had any BSODs during gaming.