It could be a few things. It could be cooling. It could be your power supply. It could be someone sold you a T-Bred "B" 2100+ (runs at 13x133) and sold it to you as a 333Mhz 2700+ (13x166). These things can be had off NewEgg for under $100 and most will do 2.2Ghz or more, but not all. Remarking CPUs used to be a big problem, but it does not happen too much anymore, but the large price differance and ease of overclocking makes it a prime target. This might be something that people might need to keep an eye out for.
You might try openning the case and blowing a house fan in there to see if it will run stable when kept slightly cooler. You might try upping the voltage a tiny bit on your CPU. It normally runs at 1.75v, but yours might take 1.8 to 1.85v to run 100% stable, but this will increase heat a bit more. Check your voltages and see if they stay stable, especially the 5v rail. These CPUs draw a lot of power and need a good stable power supply.
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