Hello Doncre, welcome to Seven Forums!
You may have a bad stick of RAM or a bad DIMM on the motherboard. Download and burn Memtesr86+ to a CD, then boot the CD and run several passes with one stick in the same DIMM to start sorting if something is bad, it will take a while so be patient and let it work. Memtest86+ Free Ram Testing Software
As it comes as an ISO file you may need the program at this link to burn it to CD. ImgBurn Free ISO Burning Software Be sure to post back with any further questions you may have and to keep us informed.