@rowangadhia this "I try an external display, nothing" in combination with this "this only seems to happen when the computer is under some sought of physical strain." it does sound like you are having an issue with the GPU or possibly even the CPU since it does freeze. Time to open it up and to check the motherboard. You also want to check, and possibly change the thermal paste, as well as clean all the air inlets etc. Just in case this is an issue with overheating. Also, try a different RAM module, make sure that yours is properly seated etc.
Use this [document|39515] to work on your Lenovo. Page 36 and on are about the fan and the heatsink. Use something like [guide|141803] for a repaste (different model, same idea).