MacBook Pro Mid-2012 starts but does not respond anymore
My gf has a severe issue with her MBP Mid-2012 (serial number is C1MK9X6ZDTY3). A few months ago I replaced the internal HD with an SSD. Everything worked fine. A new SATA cable (https://www.amazon.de/ireplacement-A1278... ) was also put in place.
Recently however the laptop had some issues. First, when pressing a certain area on the case, it would reboot. However, after rebooting I could work with it again as if nothing has happend. A few days later, it would again shut down, but then make 3 beeps while attempting to reboot. As several sources online state, this means faulty RAM. Intuitively I just tried to reboot again and the MBP worked just fine. My gf told me that there were cases where the diplays showed some glitches. Right now the situation got worse and the laptop cannot be used anymore. It boots, but then the "spinning coloured ball" occurrs. The laptop responds extremely slow. Finder cannot be opened, etc.
One more thing: She just told me that a few weeks ago she switched on the laptop with the power cable connected because the battery was empty. She then noticed some sort of "short circuit" when connected the cable. There was a tiny flash and it was as if something "burned". The funny thing is just that I would expect that the laptop immediately stops working. However it worked fine afterwards, but (obviously) slowly deteriorated as described above.
Other things I have tried:
- I run Apple diagnostics. It said there could be an issue with the battery. I then did it again with power cable attached and it said there are no problems.
- I removed both memory sticks (one by one) to ensure that none of them are faulty. With only one of them in use, the system behaved in the same erroneous way.
So what whould I do now? Can I do anything at all or should I go to a technician? Which faulty hardware could be responsible for the described behavior?