Firefox and IE pop ups of "walmart gift card winner"

I was reading through posts and found a VERY similar post that sounds like an identical problem with my own computer. It said it was the myonlinearcade malware. My firefox sometimes refuses to open, closes suddenly, won't open webpages found from search engines, and opens a "you won a walmart gift card" pop up ALL the time. I need help fixing this or I will be forced to buy a new computer. Thank you!