Hi and welcome to TSF you could take the side of and check all the cables and connections are firmly and correctly seated,do the same with the ram and videocard,then check the heatsink and fan sits on top of the cpu,get a can of compressed air and blow out all the dust and debris from the heatsink and fan and the airvents and case be carefull around the fan use a straw or similar to prevent the fan turning and remember safety first so switch off and unplug the power from the computer and ground yourself either with a wrist strap or by touching the bare unpainted part of the case,is this your machine Gateway Support - Specifications upgrading the power supply should be a priority a minimum 550w or better,A good known brand you can find info on many here http://www.techsupportforum.com/forums/f210/power-supply-information-and-selection-192217.html