Solved! As I suspected and as suggested by many of you, the problem seems to be my old GPU. I have 2 GPUs but to isolate the problem I removed one of them and everything worked perfect albeit using 1 monitor. I increased all settings in MSFS to the max (within1920x1080) The temperature was low and and the functions were fast even multi-tasking. I replaced my old card and the error message came back! I took my old card completely apart, profusely cleaned it specially the fan, removed & replaced the thermal paste in the GPU processor, cleaned the contacts and replaced it. Everything works perfect! My 3 monitors are back, I went beyond the max settings on MSFS ran it while multitasking with Photo Shop, Premiere Pro and Maya and had NO problems.
Thanks to everyone for their help and suggestions which I implemented one by one, maybe those were part of the overall solution....