Dell inspiron 1521 screen changes colors

good day all,

I have a Dell Inspiron 1521, after around 15 minutes by screen begins to have lines and then little squares that changes colors and then after 2-3 minutes the screen goes black. then I proceeded to shut down and restart under safe mode. then restart again and it appears fine until around 3-0-45 minutes it does it again. My assumption is that it means my video card is going. any ideas please advise