Hi there! This is my first post on Mac Rumors, I hope to find some help here with my problems on this Macbook Pro (Mid 2012). So my brother came to me with his Macbook Pro, it used to run smoothly with no issues until one day. Now it has very long boot times and a lot of lag with the spinning wheel running. Starting up apps takes very long, it's very annoying to work with. I had this problem before with my own device and even with other Macbook Pro's I fixed, every time it was the hard drive that was failing so I replaced it with a new SSD. I did the same with my brother's Macbook Pro but this didn't solve the problems it had. The installation (bootable USB) took very long, I think like 4-5 hours. After installation the boot time is even slower then before and it still has the same performance problems. If I connect the original HDD through an USB/SATA cable it still has the same symptoms. So the problem isn't the hard drive, ssd or internal sata cable. After this I did a PRAM and SMC reset, this didn't help either. The Apple Hardware Test didn't detect any problems. I don't know what to do next. Can anyone here help me with this? I hope it's not something like logic board/cpu failure. Thanks in advance!