One thing you do not mention as having been replaced is the PSU for the computer.
The power requirements of the new motherboard, CPU, Graphics card and RAM may be on the limits of (or even exceed) what the PSU can supply and, if it was already on the way out, replacing the other components could have made your symptoms worse.
> For a long time, I have had trouble out of the actual computer unit in my cabinet.
> I've swapped nearly everything:
> - Motherboard
> - Arcade VGA Card
> - Processor & RAM
> - Reformatted
> And it STILL is showing the same symptoms:
> - Random Game crashes
> - Random Reboots
> - Random Blue Screens
> - Random program crashes
> This has been going on for years.... and it is mostly unplayed because of these
> And last night I had a thought.... what about EMI? My motherboard is mounted sideways
> and it merely 15 or so inches away from the arcade monitor with no shielding. Could
> this be what is causing my problems?