Causes can include: inadequate amount of memory... 512 mb or under, or bad memory module (download and run free MemTest86 for 4 hours or 7 passes, whichever is longer); inadequate or too much thermal paste on heat sink; bad or wobbly cpu fan; incorrect driver for video graphics card; problem with Service pack 3 related to drivers; inadequate power supply in constant output of amperage (from cheap or off-brands); heat issue someplace; loose cable (remove and reseat everything); or a defective optical drive (very common problem these days).
Look in your Start->Control Panel->System->Hardware->Device Manager to see if the Device Manager is reporting any yellow or red flags.
Get a power supply tester ($10 to $25 depending on quality) to take a closer look at your power supply.
Look at thermal paste. It should be just barely enough. Too much acts as an insulator.
Your equipment listed is good and known to be reliable, and you have enough memory (but one module could be bad, so download and run the free and very good MemTest86 for four hours or 7 passes, whichever is longer.). Tell us about your video graphics card, and other PCI-e or PCI components installed..
In repair service, we find the number one problem is drivers, but it could be for any device so may take some time to track down and test.
You might want to consider dropping back to the most fundamental install... video - floppy drive or other simple program install off a flash or CD; and one memory module. Boot and run for an hour. Then change memory module... and so it goes until you have given all the simple stuff time to fail. Then add or change a component one at a time.
Next time it crashes, try rebooting immediately. Does it happen again immediately. If so, try SAFE MODE. If it works in safe mode, it is likely something to do with the video graphics card or driver.
Good luck. Please let us know how it all turns out.
