Do videogames actually lower grades?

ok so i've owned a 360 for 2 years now and have never had this problem. i'm suddenly playing cod4 like crazy, i cant stop. im a 9th prestige level 40 and cant stop. some of my grades have lowered a bit in 8th grade. i have a c on my midterm now and on my last reportcard. i've made honor roll all of 6th and 7th grade, and now i only so far have made it 1 out of the 3 times in 8th. the 2nd trimester i didn't make it and i want to make it the 3rd. please help i have a real problem. i dont even have a girlfriend! HELP!!!!!!!!!!!!