My 2012 MacBook pro 13 just came back from repairs. It wouldn't turn on. It happend after I plugged in my mobile broadband from t mobile. I didn't think it was the culprit. But i plugged it in after getting it back again and it won't turn on again. Now I'm thinking it may be the cause. However do I have to be extra cautions now whenever i buy a new USB device? Not only that how can i know if a USB device to going to fry my machine or not? I'm incredibly frustrated right now. I've been a PC girl my whole and never had such problems with laptops. Ive been with apple for 3 weeks and nothing but problems.