If you're getting computation errors that can't be explained away, there's several things you can do to isolate the cause.
Sometimes the cause is operational: i.e., you start playing a complex game which ends up adversely affecting the resources available, which causes the WU to error out due to failed memory allocation requests. Usually, however, it's fairly obvious when that happens.
Or there could be a real probelm with your computer. Even "stock" computers degrade over time. A great example is simple dust. Given enough time, dust will clog the CPU heatsink, rendering the CPU fan much less effective than it was originally. The resulting thermal problems will cause a variety of hard to diagnose problems.
So, things I would suggest you try:
1) Open up the computer and clean out any dust with either a vacuum or compressed air. One computer in my kids' room actually stopped working because of this. (Shame on me.) In my bedroom, I've found that talcum particles (thanks, wife!) tend to cause more rapid dust buildup in my computer now that it's in the bedroom than when it was in the basement. The result was less efficient cooling, which caused the fans to run faster, which caused the wife to complain, which caused me to clean out the computer. That's what we call in engineering circles "closed loop". :)
2) Run a memory diagnostic on your system. I'll leave it to someone else to suggest a good one. Sometimes a DIMM just goes bad. (I wish PCs still used parity memory. ::sigh::)
3) Run CoreTemp or some other CPU temperature monitoring program so you have an idea of how hot your system is running. Stock systems usually have relatively poor CPU cooling, and when you run them 24/7 at 100%, through in some adverse environmental conditions (warm room, restricted ventilation, dusty, etc.), and you might be looking at a computer that's just running too warm. It helps a lot to know how hot it actually is.
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