sonic heroes heeeeeeeeeeeeelp!!!!!!!!!!!

hey guys i was playing sonic heores and i had this problem. see how slow it runs?? it's at 60 fps, and when i turn it to 30 fps it runs normally
i don't think the problem is with my pc because i have an
hp D6DV6-667
processor core I7
memory 6Go
harddisk 1 tera
video memory 1 Go
please i wanna know what is causing this problem and tell me if there's any way for the game to run better