It still sounds like a hardaware problem so in etheir way or other
I think you need to check your hardware, may be your HDD?
We have one RouterOS version 2.9.50 installed on a computer
Pentium III 400MHz, and isn't causing any problem, nor CPU load.
We have simple queues running on this machine and time to time
we use it as Proxy for testing also.
As for motherboard, I think IBM with intel chipset are very steady
Don't crash the ambulance, whatever you do