Okay so my computer stays on for about 4-6 hours and always blue screens sometime between that period no matter what I do. I'm able to play games on it fine and they don't cause it to crash. Time is what seems to make it crash. I have two fans in my case and three if you include fan on heatsink.
CPU: Phenom 9850 2.50 ghz quad core
Power Supply:Ultra LSP 550w. 135mm fan. Input: AC input voltage: 115/230v. AC input frequency: 60/50hz.
Ram: 2 sticks of hynix 1gb 2Rx8 pc2 - 5300U - 555 12, 2 sticks of hynix 512mb 2Rx8 pc2 - 5300U - 555 12 (All the ram is recycled from my old computer but work)
Windows 7 ultimate 64-bit
New computer build about two weeks old stilling BSOD every 4 to 6 hours.
Not motherboard as i replaced it and still BSOD.
Caused by ntoskrnl.exe+71f00. Bug check code: 0x00000050 PAGE_FAULT_IN_NONPAGED_AREA
Caused by ntoskrnl.exe+71f00. Bug check code: 0x0000000a IRQL_NOT_LESS_OR_EQUAL
Caused by ntoskrnl.exe+71f00. Bug check code0x0000001eKMODE_EXCEPTION_NOT_HANDLE…
Caused by ntoskrnl.exe+71f00. Bug check code 0x00000050 PAGE_FAULT_IN_NONPAGED_AREA
Have a think if you have any tasks that are set up to run after 4 - 6 hours. Virus scans, indexing services when the computer is set to hibernate etc.
This is rather likely to be memory related. Like anonymous1 suggested, try running Memtest for a long period of time. If it passes ok it may very well be your hard drive that has issues. Checking SMART data for errors is a good starting place. Coupled with running a test utility from your drives manufacturer you should have an idea on if the hard drive is ok, on it's way out or bust.
If it doesn't pass what you could try doing is removing sticks of ram to identify which (if not all) are causing the issue. If it's all still failing try borrowing some ram from a friend and rerun the tests / see if the system has the same behavior. Avoid buying new ram too quickly!