Windows 7 irql_not_less_or_equal minutes after login

[VHZ11]

Hello, I am new to this forum.

My PC is having a irql_not_less_or_equal BSOD a few minutes after login in Windows 7. The only programs running are Quickbooks POS 8.0, Excel, Notepad and HWMonitor. After two or three reboots the computer runs normally.
I have tested and switched ram, no errors
Tested the hard drive, no errors
Cleaned the dust
Checked the PSU
Unistalled and clean installed several nvidia drivers in safe mode

Because of the error code: Is this a driver issue?

My system specs are:
OS: Windows 7 Ultimate x64
CPU: AMD Athlon II X3 425
Motherboard: ASUS M4N68T-M
RAM: Kingston HyperX Blu 2GB 240-Pin DDR3 SDRAM DDR3 1333
Graphics Card: Galaxy 64TGF8HX6FTZ GeForce GT 640
Hard Drive: Samsung 500 GB SATA II Hard Drive HD502HJ
PSU: LEPA N Series N500-SA 500W ATX12V Power Supply

Thank you in advance

 

[DelJo63]

The most frequent causes are 1) memory and 2) hd errors
Get a copy of MEMTEST and see what your memory is like

 

[VHZ11]

The most frequent causes are 1) memory and 2) hd errors
Get a copy of MEMTEST and see what your memory is like

I did test the ram, no errors on the current stick in use

 

[DelJo63]

YES BUT - - how thoroughly? Boot into Safe Mode and set it to run 4-5 passes; you can't test memory in a one-pass, 10 minute test.

 

[VHZ11]

YES BUT - - how thoroughly? Boot into Safe Mode and set it to run 4-5 passes; you can't test memory in a one-pass, 10 minute test.

I tested 7 passes, no errors

 

[Tmagic650]

Okay, you've tested your memory, now it's time to take a look at your Nvidia video driver or card. The BSOD's are coming from the video driver or there is an issue with the video card itself... The power supply may not be big enough or it is failing slowly

 

[VHZ11]

How do I know if the drivers, video card or psu are the cause of the problem? I have running nvidia 335.23 drivers on my other computer no problems, the PSU is fairly new, purchased 6 months ago, and the graphics card is just one month old. Both purchased new.