Sounds like you may have a short in the new monitor. I suppose a keyboard could short out and cause problems as well but the display is the more logical choice since there is quite a bit more power involved there. Have you started diagnosing the new pc yet? If its the display the gfx card prolly got nailed. Just a guess.…
It's extremely odd that your old PC should exhibit the same (or similar) symptoms with the new peripherals. They draw what little power they need from the PC, so I can't see them being the problem. Did your old PC get past the 'Power On Self Test' stage, eg did you see anything on the monitor? You're not running the…