nvlddmkm.sys and dxgmms1.sys bsod

Since 06/30/14 my PC is having bsod problems. I believe it happens twice in half an hour. I've tried everything, updating drivers, rebooting, everything. Everytime the error happened, I check WhoCrashed and it always tells me about nvlddmkm.sys. I searched, tried everything. I don't know if is a motherboard/graphics card problem, but I think you guys should know, I had to change my motherboard twice because of bsod, I'm currently using a Dell motherboard.

dxgmms1.sys (DirectX Graphics MMS, Microsoft Corporation)
nvlddmkm.sys (NVIDIA Windows Kernel Mode Driver, Version 337.88 , NVIDIA Corporation)

If no updates for these drivers are available, try searching with Google on the names of these drivers in combination the errors that have been reported for these drivers and include the brand and model name of your computer as well in the query. This often yields interesting results from discussions from users who have been experiencing similar problems.

Specs: i5 2400 3.10
GT 620 1GB DDR3
4GB RAM
500 HD

Additional information is required.

1. Download the DM Log Collector application to your desktop by clicking the link below

DM Log Collector.exe

2. Run it by double-clicking the icon on your desktop, and follow the prompts.
3. Locate the .ZIP file that is created on your desktop, and upload it here in your next reply.

Code:

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*                        Bugcheck Analysis                                    *
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Use !analyze -v to get detailed debugging information.

BugCheck 50, {fffffd7ffffffff0, 0, fffff800030f14a6, 7}


Could not read faulting driver name
Probably caused by : memory_corruption ( nt!MiUpdateWsleHash+136 )

Followup: MachineOwner
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Run 8 passes of MemTest86+

RAM - Test with Memtest86+