Short and sweet:
In my desktop computer, my motherboard and CPU were new in 2007. The other parts are newer, the HDD was installed in 2011 and still is fine, the power supply is brand-new (less than a week old), the optical drive is about 5 years old but still works fine.
According to the repair shop I spoke to, it would be impossible to simply replace the motherboard, CPU, and RAM with new ones, and I really should just get a new computer. And then they quoted me 800 bucks for a custom build.
So… is it impossible? Why or why not? He said something about it not working with my existing case (?), but I don’t get why a new motherboard / CPU wouldn’t work with my existing hardware which is still relatively new. I don’t know enough about hardware to know if this is a scam or what.