|I prefer Antec or PC Power & Cooling power supplies.|
Someone said they doubt the memory is the issue. However, if removing it causes things to work better, it just might be. Check your mo/bo specs, it may REQUIRE 2 DIMMS before it will boot properly.
Make sure everything is hooked up properly. Make sure the cooling fan is installed and operating. As stated, make sure the thermal transfer paste is used and used properly.
If you have a multimeter, check the output of the power supply, maybe it's cutting in and out, or swap it with a known good unit.