Can't access other websites except for google, youtube, and other video streaming sites

this began on tuesday july 09, i left my home on july 07 and bc we wouldn't be home for 2 days i unplugged our xfinity modem. I tried plugging it back in to use my internet like usual, all other websites except for video streaming sites fail to work. please help, i have a technician coming this saturday but want to know if there's something i can do on my end to fix it.