Shift and alt keys not working on blackwidow tournament edition stealth

Out of the blue one day they just stopped working. Nothing like this had ever happened before on the keyboard, I got it second hand and cleaned out the hairs in it months ago and it's affected both shifts and alts on both sides so it can't be a problem with the switches. It can't be a problem with the OS either because I was on mac when it happened and the shift was working on the macbook keyboard and I tried windows and the same there. Do you know how I could fix this problem. It's really bad because I can't play many games now.