My macbook pro keeps freezing

hello. I have just recieved my used mid 2010 macbook pro 15" from Maple UK. It works fine except After two minutes of usage it makes a god awful grinding noise, freezes for a second and restarts. I already turned off automatic graphic switch from energy saver, it ran longer (about 10 minutes) before the same happened. What should i do now? I paid a lot for this and i actually need this for work, thank you.