Sounds like an overheating problem for sure. Is the fan running at all? Open the case and let a fan blow in there and see if it helps.
Also you may want to go into the BIOS and see if you can change your fan settings. You may have defaulted to "off" when you reformatted. Most can be set to "always on" or a few other options.
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If your equation requires either a complex combination of variables to get the desired result OR you can't seem to get the result regardless of the variables....it ain't your variables, it's your constant.