touchscreen problems

Okay so i just bought this phone xrfrom a guy yesterday and it worked fine but he did warn me that it sometimes would freeze and the touchscreen didn’t work at all but the buttons like not on the touchscreen did work and it happened to me about 4 times and they only lasted for a few minutes and now this one is still lasting and it’s been 6 hours anyone have any idea what this is and how to fix it?