Hi, everyone. I'm new here and in desperate need of help. I switched over to Yosemite a couple months ago from Mountain Lion and have had nothing but issues since. I currently have a mid-2012, 13-inch, non-retina Macbook Pro that I just upgraded to 8GB yesterday, being assured it would fix the issues I've been having. Unfortunately, that wasn't the case. Since switching to Yosemite, I have had constant issues with startup and performance. Often upon startup, it will get hung up at around the half way point and refuses to boot. Other times, it will start up, but I won't have a menu bar or dock. When it does start up successfully, I have about 15 minutes of use before I get the rainbow wheel and the laptop has to be left for an extended amount of time before it will run smoothly again (often an hour or two), only to begin the cycle over again. Finder will freeze, as will every other app I attempt to use. Safari will sometimes open, sometimes it won't. If it does, I have major performance issues (cursor lag, freezing, etc.). I've switched to Chrome because it will typically open dependably, but I still run into performance and freezing issues. Firefox won't even open. I don't dare attempt to open apps like calendar or mail, because it freezes my computer instantly, and I get an error message that it shut down unexpectedly. Word also has major issues of the same sort, but will open most of the time, although I have issues with freezing. Upon upgrading to 8GB yesterday, I was assured it would fix these problems, but they have since gotten worse. I now only have a couple minutes of smooth performance before I get the rainbow wheel. They cleaned my hard drive (I am nowhere near storage capacity) and tested all hardware, which is working fine. I am currently writing a thesis, and this laptop is my lifeline. I just bought it a little over a year ago. Does anyone have any suggestions on how these issues can be fixed? I apologize, but I am not very tech-savvy, so I don't understand a lot of advanced terminology. Thank you so much.