Well, you could raise the BIOS temperature limit before shutoff for starters, but I'd advise you regulate your temperatures to make sure it isn't overheating much anyway, as it's not good for the PC. There's plenty of free tools to do this, a quick Google search will reveal the best options.
If it isn't overheating in any way, then it's possibly a bad DIMM or an old PSU. These may need replacing.