I was watching a YouTube video when my screen froze and started glitching. After a few minutes i shuted it down completely. Now it will not finish starting up and a white screen appears with red pixels on it. What is this and what should i do?
iMac
Welcome Victoria!
iMacs has been in continuous production since 1998 in four broad families based on different hardware configurations. Therefore need more info to effectively help you. Although more details may be needed later, a good place to start is for you to tell us your processor type and you Mac OS version, both easily available by doing "About this Mac..." from your Apple menu at the left end of your menu bar.
Of the two iMac forums, this is for the old one made before 2006. If you have a newer model we can ask the Hosts to move you to the more active forum.
Screen froze while starting up and red pixels appear
