Costco sells 6 packs for cheap. But any electronics or computer store should carry them. Just make sure you give the heatsinks and electrical caps a good dusting and hopefully, that will solve your problem. Next step is to reapply the heatsink paste, then after that, PSU and RAM could be culprits. biggles604 did provide a good tip of monitoring the voltage rails in the BIOS to make sure they are not under or over volting.
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