Do you have good airflow through your case, i.e. front-to-back and/or bottom-to-top? If not, add or adjust your fans so you do.
What PSU do you have? I'm also assuming a typo, so it's really 1000W or 1100W, but what brand and model? For example, if it's a Diablotek, it's a wonder it hasn't burned, but it is probably going out of spec and bad voltages are causing your shutdowns.