Acer Aspire M3802

Acer Aspire M3802 boots up then after about 10 minutes I lose video, kb and mouse. Won’t come back on until I reseat memory then comes on for 10 minutes then off again. I have tried new video card, power supply and memory. What should i try next? I was going to order a new motherboard but hate to put out that money unless for sure it’s that.