Hi, Any helps would be appreciated. I haven't taken my broken MP to be serviced yet. I have a MP4.1 that's been upgraded to 5.1. The processor is a W3590 there's 24 gigs of memory and I have an Accelsior for OSX and Crucial M4 for Windows. The GFX card is a GTX 680 Mac Edition. The MP has worked flawlessly for over 5 years until now. I did a clean install of Yosemite. I accidentally formatted the Windows drive in the process. Yosemite worked fine but things got messed up when I tried to reinstall Windows 8. I did some internal fiddling before doing the reinstall (detaching file HDD's etc.) When installing Windows I couldn't get the installation to continue after the first required boot during the installation. When I went to OSX programs started very slowly. For example Safari could take a minute and have the beach ball spinning all the time. There where these stops even after the program started. Sometimes (but not often or consistanty) OSX would crash. I tried reinstalling Yosemite but I can't get the installation to complete. At this moment I have no OS installed. I'm trying one last time and currently Yosemite has been installing for 4 hours but seems to proceed (though very slowly) I already tried checking that all the cables internally and externally are connected. I've also disconnected all the devices that are not absolutely necessary. I disconnected some of the RAM modules and then changing between modules to rule out the possibility of a broken memory module - it didn't help. Does this sound familiar to any known hardware or software problem? What bootable software should I use to try to find hardware problems? EDIT: The installation/restore of OS X finally went through. Beach balls still keep spinning but I guess I could use diagnostic tools designed for OS X.