2008 MacBook Computer

I've had this PC for many years. I even upgraded its internal memory by 500 GB, bringing the total to 1 TB. It shows very few signs of wear for its age and has been well maintained. However, it now fails to boot properly. Sometimes it emits the SOS signal in Morse code for a while before starting up normally. Other times, it remains stuck on the SOS code for too long. The shop where I took it for repair said they couldn't work on the motherboard because it's a Mac. Therefore, there must be some issue with the motherboard that could be easily fixed by someone familiar with it. When it does boot, the computer functions perfectly and is a powerhouse.